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House Robber - Maximum possible stolen value

Last Updated : 01 Oct, 2024
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There are n houses built in a line, each of which contains some money in it. A robber wants to steal money from these houses, but he can’t steal from two adjacent houses. The task is to find the maximum amount of money which can be stolen.

Examples: 

Input: hval[] = {6, 7, 1, 3, 8, 2, 4}
Output: 19
Explanation: The thief will steal from house 1, 3, 5 and 7, total money = 6 + 1 + 8 + 4 = 19.

Input: hval[] = {5, 3, 4, 11, 2}
Output: 16
Explanation: Thief will steal from house 1 and 4, total money = 5 + 11 = 16.

Given an array, the solution is to find the maximum sum subsequence where no two selected elements are adjacent

[Naive Approach] Using Recursion- O(2n) Time and O(n) Space

The idea is to explore all the possibilities for each house using Recursion. We can start from the last house and for each house, we have two choices:

  1. Rob the current house and skip the house just before it.
  2. Skip the current house and move to the next house.

So, the recurrence relation will be:

maxLootRec(n) = max(hval[n - 1] + maxLootRec(n - 2), maxLootRec(n - 1)),
where maxLootRec(n) returns the maximum amount of money which can be stolen if n houses are left.

C++
// C++ Program to solve House Robber Problem using Recursion

#include <iostream>
#include <vector>
using namespace std;

// Calculate the maximum stolen value recursively
int maxLootRec(vector<int> &hval, int n) {
	
    // If no houses are left, return 0.
    if (n <= 0)  return 0;
  
  	// If only 1 house is left, rob it. 
    if (n == 1)  return hval[0];

    // Two Choices: Rob the nth house and do not rob the nth house 
    int pick = hval[n - 1] + maxLootRec(hval, n - 2);
    int notPick = maxLootRec(hval, n - 1);

    // Return the max of two choices
    return max(pick, notPick);
}

// Function to calculate the maximum stolen value
int maxLoot(vector<int>& hval) {
    int n = hval.size();
  
    // Call the recursive function for n houses
  	return maxLootRec(hval, n);
}

int main() {
    vector<int> hval = {6, 7, 1, 3, 8, 2, 4};
    cout << maxLoot(hval);
    return 0;
}
C
// C Program to solve House Robber Problem using Recursion

#include <stdio.h>

// Function to calculate the maximum stolen value
int maxLoot(int *hval, int n) {
    
    // If no houses are left, return 0.
    if (n <= 0)  return 0;
  
    // If only 1 house is left, rob it. 
    if (n == 1)  return hval[0];

    // Two Choices: Rob the nth house and do not rob the nth house 
    int pick = hval[n - 1] + maxLoot(hval, n - 2);
    int notPick = maxLoot(hval, n - 1);

    // Return the max of two choices
    return (pick > notPick) ? pick : notPick;
}

int main() {
    int hval[] = {6, 7, 1, 3, 8, 2, 4};
    int n = sizeof(hval) / sizeof(hval[0]);
    printf("%d\n", maxLoot(hval, n));
    return 0;
}
Java
// Java Program to solve House Robber Problem using Recursion

class GfG {
  
    // Calculate the maximum stolen value recursively
    static int maxLootRec(int[] hval, int n) {
    
        // If no houses are left, return 0.
        if (n <= 0) return 0;
      
        // If only 1 house is left, rob it. 
        if (n == 1) return hval[0];

        // Two Choices: Rob the nth house and do not rob the nth house 
        int pick = hval[n - 1] + maxLootRec(hval, n - 2);
        int notPick = maxLootRec(hval, n - 1);

        // Return the max of two choices
        return Math.max(pick, notPick);
    }

    // Function to calculate the maximum stolen value
    static int maxLoot(int[] hval) {
        int n = hval.length;
      
        // Call the recursive function for n houses
        return maxLootRec(hval, n);
    }

    public static void main(String[] args) {
        int[] hval = {6, 7, 1, 3, 8, 2, 4};
        System.out.println(maxLoot(hval));
    }
}
Python
# Python Program to solve House Robber Problem using Recursion

# Calculate the maximum stolen value recursively
def maxLootRec(hval, n):
    
    # If no houses are left, return 0.
    if n <= 0:
        return 0
  
    # If only 1 house is left, rob it. 
    if n == 1:
        return hval[0]

    # Two Choices: Rob the nth house and do not rob the nth house 
    pick = hval[n - 1] + maxLootRec(hval, n - 2)
    notPick = maxLootRec(hval, n - 1)

    # Return the max of two choices
    return max(pick, notPick)

# Function to calculate the maximum stolen value
def maxLoot(hval):
    n = len(hval)
  
    # Call the recursive function for n houses
    return maxLootRec(hval, n)

if __name__ == "__main__":
    hval = [6, 7, 1, 3, 8, 2, 4]
    print(maxLoot(hval))
C#
// C# Program to solve House Robber Problem using Recursion

using System;

class GfG {
    
    // Calculate the maximum stolen value recursively
    static int MaxLootRec(int[] hval, int n) {
        
        // If no houses are left, return 0.
        if (n <= 0) return 0;

        // If only 1 house is left, rob it. 
        if (n == 1) return hval[0];

        // Two Choices: Rob the nth house and do not rob the nth house 
        int pick = hval[n - 1] + MaxLootRec(hval, n - 2);
        int notPick = MaxLootRec(hval, n - 1);

        // Return the max of two choices
        return Math.Max(pick, notPick);
    }

    // Function to calculate the maximum stolen value
    static int MaxLoot(int[] hval) {
        int n = hval.Length;

        // Call the recursive function for n houses
        return MaxLootRec(hval, n);
    }

    static void Main() {
        int[] hval = { 6, 7, 1, 3, 8, 2, 4 };
        Console.WriteLine(MaxLoot(hval));
    }
}
JavaScript
// JavaScript Program to solve House Robber Problem using Recursion

// Calculate the maximum stolen value recursively
function maxLootRec(hval, n) {
    
    // If no houses are left, return 0.
    if (n <= 0) return 0;
  
    // If only 1 house is left, rob it. 
    if (n === 1) return hval[0];

    // Two Choices: Rob the nth house and do not rob the nth house 
    let pick = hval[n - 1] + maxLootRec(hval, n - 2);
    let notPick = maxLootRec(hval, n - 1);

    // Return the max of two choices
    return Math.max(pick, notPick);
}

// Function to calculate the maximum stolen value
function maxLoot(hval) {
    let n = hval.length;
  
    // Call the recursive function for n houses
    return maxLootRec(hval, n);
}

let hval = [6, 7, 1, 3, 8, 2, 4];
console.log(maxLoot(hval));

Output
19

Time Complexity: O(2n). Every house has 2 choices to pick and not pick.
Auxiliary Space: O(n). For recursion stack space

[Better Approach] Using Memoization - O(n) Time and O(n) Space

The above solution has optimal substructure and overlapping subproblems. See the below recursion tree, maxLootRec(2) is being evaluated twice.

Recursion-Tree-for-House-Robber
Recursion Tree for House Robber

We can optimize this solution using a memo array of size (n + 1), such that memo[i] represents the maximum value that can be collected from first i houses. Please note that there is only one parameter that changes in recursion and the range of this parameter is from 0 to n.

C++
// C++ Program to solve House Robber Problem using Memoization

#include <iostream>
#include <vector>
using namespace std;

int maxLootRec(const vector<int>& hval, int n, vector<int>& memo) {
  
    if (n <= 0) return 0;
    if (n == 1) return hval[0];

    // Check if the result is already computed
    if (memo[n] != -1) return memo[n];

    int pick = hval[n - 1] + maxLootRec(hval, n - 2, memo);
    int notPick = maxLootRec(hval, n - 1, memo);

    // Store the max of two choices in the memo array and return it
    memo[n] = max(pick, notPick);
    return memo[n];
}

int maxLoot(vector<int>& hval) {
    int n = hval.size();
  
    // Initialize memo array with -1
    vector<int> memo(n + 1, -1); 
    return maxLootRec(hval, n, memo);
}

int main() {
    vector<int> hval = {6, 7, 1, 3, 8, 2, 4};
    cout << maxLoot(hval);
    return 0;
}
C
// C Program to solve House Robber Problem using Memoization

#include <stdio.h>
#include <stdlib.h>

int maxLootRec(const int* hval, int n, int* memo) {
  
    if (n <= 0) return 0;
    if (n == 1) return hval[0];

    // Check if the result is already computed
    if (memo[n] != -1) return memo[n];

    int pick = hval[n - 1] + maxLootRec(hval, n - 2, memo);
    int notPick = maxLootRec(hval, n - 1, memo);

    // Store the max of two choices in the memo array and return it
    memo[n] = (pick > notPick) ? pick : notPick;
    return memo[n];
}

int maxLoot(int* hval, int n) {
    
    // Initialize memo array with -1
    int memo[n + 1];
    for (int i = 0; i <= n; ++i) {
        memo[i] = -1;
    }
  
    int result = maxLootRec(hval, n, memo);
    return result;
}

int main() {
    int hval[] = {6, 7, 1, 3, 8, 2, 4};
    int n = sizeof(hval) / sizeof(hval[0]);
    printf("%d\n", maxLoot(hval, n));
    return 0;
}
Java
// Java Program to solve House Robber Problem using Memoization

import java.util.Arrays;

class GfG {
    static int maxLootRec(int[] hval, int n, int[] memo) {
        if (n <= 0) return 0;
        if (n == 1) return hval[0];

        // Check if the result is already computed
        if (memo[n] != -1) return memo[n];

        int pick = hval[n - 1] + maxLootRec(hval, n - 2, memo);
        int notPick = maxLootRec(hval, n - 1, memo);

        // Store the max of two choices in the memo array and return it
        memo[n] = Math.max(pick, notPick);
        return memo[n];
    }

    // Function to calculate the maximum stolen value
    static int maxLoot(int[] hval) {
        int n = hval.length;
      
        // Initialize memo array with -1
        int[] memo = new int[n + 1];
        Arrays.fill(memo, -1);

        return maxLootRec(hval, n, memo);
    }

    public static void main(String[] args) {
        int[] hval = {6, 7, 1, 3, 8, 2, 4};
        System.out.println(maxLoot(hval));
    }
}
Python
# Python Program to solve House Robber Problem using Memoization

def maxLootRec(hval, n, memo):
    if n <= 0:
        return 0
    if n == 1:
        return hval[0]

    # Check if the result is already computed
    if memo[n] != -1:
        return memo[n]

    pick = hval[n - 1] + maxLootRec(hval, n - 2, memo)
    notPick = maxLootRec(hval, n - 1, memo)

    # Store the max of two choices in the memo array and return it
    memo[n] = max(pick, notPick)
    return memo[n]

def maxLoot(hval):
    n = len(hval)
  
    # Initialize memo array with -1
    memo = [-1] * (n + 1)
    return maxLootRec(hval, n, memo)

if __name__ == "__main__":
    hval = [6, 7, 1, 3, 8, 2, 4]
    print(maxLoot(hval))
C#
// C# Program to solve House Robber Problem using Memoization

using System;
class GfG {
    static int MaxLootRec(int[] hval, int n, int[] memo) {
        if (n <= 0) return 0;
        if (n == 1) return hval[0];

        // Check if the result is already computed
        if (memo[n] != -1) return memo[n];

        int pick = hval[n - 1] + MaxLootRec(hval, n - 2, memo);
        int notPick = MaxLootRec(hval, n - 1, memo);

        // Store the max of two choices in the memo array and return it
        memo[n] = Math.Max(pick, notPick);
        return memo[n];
    }

    // Function to calculate the maximum stolen value
    static int MaxLoot(int[] hval) {
        int n = hval.Length;

        // Initialize memo array with -1
        int[] memo = new int[n + 1];
        for (int i = 0; i <= n; i++) {
            memo[i] = -1;
        }

        return MaxLootRec(hval, n, memo);
    }

    static void Main() {
        int[] hval = { 6, 7, 1, 3, 8, 2, 4 };
        Console.WriteLine(MaxLoot(hval));
    }
}
JavaScript
// JavaScript Program to solve House Robber Problem using Memoization

function maxLootRec(hval, n, memo) {
    if (n <= 0) return 0;
    if (n === 1) return hval[0];

    // Check if the result is already computed
    if (memo[n] !== -1) return memo[n];

    const pick = hval[n - 1] + maxLootRec(hval, n - 2, memo);
    const notPick = maxLootRec(hval, n - 1, memo);

    // Store the max of two choices in the memo array and return it
    memo[n] = Math.max(pick, notPick);
    return memo[n];
}

// Function to calculate the maximum stolen value
function maxLoot(hval) {
    const n = hval.length;
  
    // Initialize memo array with -1
    const memo = new Array(n + 1).fill(-1);
    return maxLootRec(hval, n, memo);
}

const hval = [6, 7, 1, 3, 8, 2, 4];
console.log(maxLoot(hval));

Output
19

Time Complexity: O(n). Every house is computed only once.
Auxiliary Space: O(n). For recursion stack space and memo array.

[Expected Approach 1] Using Tabulation - O(n) Time and O(n) Space

The idea is to build the solution in bottom-up manner. We create a dp[] array of size n+1 where dp[i] represents the maximum value that can be collected with first i houses. We first fill the known values, dp[0] and dp[1] and then fill the remaining values using the formula: dp[i] = max(hval[i] + dp[i - 2], dp[i - 1]). The final result will be stored at dp[n].

C++
// C++ Program to solve House Robber Problem using Tabulation

#include <iostream>
#include <vector>
using namespace std;

// Function to calculate the maximum stolen value using bottom-up DP
int maxLoot(vector<int>& hval) {
    int n = hval.size();
  
    // Create a dp array to store the maximum loot at each house
    vector<int> dp(n+1, 0);

    // Base cases
    dp[0] = 0;
    dp[1] = hval[0];

    // Fill the dp array using the bottom-up approach
    for (int i = 2; i <= n; i++) 
        dp[i] = max(hval[i - 1] + dp[i - 2], dp[i - 1]);

    return dp[n];
}

int main() {
    vector<int> hval = {6, 7, 1, 3, 8, 2, 4};
    cout << maxLoot(hval) << endl;
    return 0;
}
C
// C Program to solve House Robber Problem using Tabulation

#include <stdio.h>

int max(int a, int b) {return (a > b) ? a : b;}
                       
int maxLoot(int* hval, int n) {
  
    // Create a dp array to store the
    // maximum loot at each house
    int dp[n+1];
    dp[0] = 0;
    dp[1] = hval[0];

    // Fill the dp array using the
    // bottom-up approach
    for (int i = 2; i <= n; i++) 
        dp[i] = max(hval[i - 1] + dp[i - 2], dp[i - 1]);

    return dp[n];
}

int main() {
    int hval[] = {6, 7, 1, 3, 8, 2, 4};
    int n = sizeof(hval) / sizeof(hval[0]);
    printf("%d\n", maxLoot(hval, n));
    return 0;
}
Java
// Java Program to solve House Robber Problem using Tabulation

class GfG {

    // Function to calculate the maximum stolen value using bottom-up DP
    static int maxLoot(int[] hval) {
        int n = hval.length;
      
        // Create a dp array to store the maximum loot at each house
        int[] dp = new int[n + 1];

        // Base cases
        dp[0] = 0;
        dp[1] = hval[0];

        // Fill the dp array using the bottom-up approach
        for (int i = 2; i <= n; i++) {
            dp[i] = Math.max(hval[i - 1] + dp[i - 2], dp[i - 1]);
        }
        return dp[n];
    }

    public static void main(String[] args) {
        int[] hval = {6, 7, 1, 3, 8, 2, 4};
        System.out.println(maxLoot(hval));
    }
}
Python
# Python Program to solve House Robber Problem using Tabulation

def maxLoot(hval):
    n = len(hval)
  
    # Create a dp array to store the maximum loot at each house
    dp = [0] * (n + 1)

    # Base cases
    dp[0] = 0
    dp[1] = hval[0]

    # Fill the dp array using the bottom-up approach
    for i in range(2, n + 1):
        dp[i] = max(hval[i - 1] + dp[i - 2], dp[i - 1])

    return dp[n]

hval = [6, 7, 1, 3, 8, 2, 4]
print(maxLoot(hval))
C#
// C# Program to solve House Robber Problem using Tabulation

using System;

class GfG {
    
    // Function to calculate the maximum stolen value using bottom-up DP
    static int MaxLoot(int[] hval) {
        int n = hval.Length;
      
        // Create a dp array to store the maximum loot at each house
        int[] dp = new int[n + 1];

        // Base cases
        dp[0] = 0;
        dp[1] = hval[0];

        // Fill the dp array using the bottom-up approach
        for (int i = 2; i <= n; i++) {
            dp[i] = Math.Max(hval[i - 1] + dp[i - 2], dp[i - 1]);
        }
        return dp[n];
    }

    static void Main() {
        int[] hval = { 6, 7, 1, 3, 8, 2, 4 };
        Console.WriteLine(MaxLoot(hval));
    }
}
JavaScript
// JavaScript Program to solve House Robber Problem using Tabulation

function maxLoot(hval) {
    const n = hval.length;
  
    // Create a dp array to store the maximum loot at each house
    const dp = new Array(n + 1).fill(0);

    // Base cases
    dp[0] = 0;
    dp[1] = hval[0];

    // Fill the dp array using the bottom-up approach
    for (let i = 2; i <= n; i++) 
        dp[i] = Math.max(hval[i - 1] + dp[i - 2], dp[i - 1]);

    return dp[n];
}

const hval = [6, 7, 1, 3, 8, 2, 4];
console.log(maxLoot(hval));

Output
19

Time Complexity: O(n), Every house is computed only once.
Auxiliary Space O(n), We are using a dp array of size n.

[Expected Approach 2] Space-Optimized DP - O(n) Time and O(1) Space

On observing the dp[] array in the previous approach, it can be seen that the answer at the current index depends only on the last two values. In other words, dp[i] depends only on dp[i - 1] and dp[i - 2]. So, instead of storing the result in an array, we can simply use two variables to store the last and second last result.

C++
// C++ Program to solve House Robber Problem using 
// Space Optimized Tabulation

#include <iostream>
#include <vector>
using namespace std;

// Function to calculate the maximum stolen value
int maxLoot(vector<int> &hval) {
    int n = hval.size();

    if (n == 0)
        return 0;
    if (n == 1)
        return hval[0];

    // Set previous 2 values
    int secondLast = 0, last = hval[0];

    // Compute current value using previous two values
    // The final current value would be our result
    int res;
    for (int i = 1; i < n; i++) {
        res = max(hval[i] + secondLast, last);
        secondLast = last;
        last = res;
    }
    return res;
}

int main() {
    vector<int> hval = {6, 7, 1, 3, 8, 2, 4};
    cout << maxLoot(hval) << endl;
    return 0;
}
C
// C Program to solve House Robber Problem using 
// Space Optimized Tabulation

#include <stdio.h>

int max(int a, int b) { return (a > b) ? a : b; }

// Function to calculate the maximum stolen value
int maxLoot(int hval[], int n) {
    if (n == 0)
        return 0;
    if (n == 1)
        return hval[0];

    // Set previous 2 values
    int secondLast = 0, last = hval[0];

    // Compute current value using previous
    // two values. The final current value
    // would be our result
    int res;
    for (int i = 1; i < n; i++) {
        res = max(hval[i] + secondLast, last);
        secondLast = last;
        last = res;
    }

    return res;
}

int main() {
    int hval[] = {6, 7, 1, 3, 8, 2, 4};
    int n = sizeof(hval) / sizeof(hval[0]);
    printf("%d\n", maxLoot(hval, n));
    return 0;
}
Java
// Java Program to solve House Robber Problem using 
// Space Optimized Tabulation

import java.util.Arrays;

class GfG {

    // Function to calculate the maximum stolen value
    static int maxLoot(int[] hval) {
        int n = hval.length;

        if (n == 0)
            return 0;
        if (n == 1)
            return hval[0];

        // Set previous 2 values
        int secondLast = 0, last = hval[0];

        // Compute current value using previous
        // two values. The final current value
        // would be our result
        int res = 0;
        for (int i = 1; i < n; i++) {
            res = Math.max(hval[i] + secondLast, last);
            secondLast = last;
            last = res;
        }

        return res;
    }

    public static void main(String[] args) {
        int[] hval = {6, 7, 1, 3, 8, 2, 4};
        System.out.println(maxLoot(hval));
    }
}
Python
# Python Program to solve House Robber Problem using 
# Space Optimized Tabulation

# Function to calculate the maximum stolen value
def maxLoot(hval):
    n = len(hval)

    if n == 0:
        return 0
    if n == 1:
        return hval[0]

    # Set previous 2 values
    secondLast = 0
    last = hval[0]

    # Compute current value using previous two values
    # The final current value would be our result
    res = 0
    for i in range(1, n):
        res = max(hval[i] + secondLast, last)
        secondLast = last
        last = res

    return res

hval = [6, 7, 1, 3, 8, 2, 4]
print(maxLoot(hval))
C#
// C# Program to solve House Robber Problem using 
// Space Optimized Tabulation

using System;

class GfG {
    
    // Function to calculate the maximum stolen value
    static int maxLoot(int[] hval) {
        int n = hval.Length;

        if (n == 0)
            return 0;
        if (n == 1)
            return hval[0];

        // Set previous 2 values
        int secondLast = 0, last = hval[0];

        // Compute current value using previous two values
        // The final current value would be our result
        int res = 0;
        for (int i = 1; i < n; i++) {
            res = Math.Max(hval[i] + secondLast, last);
            secondLast = last;
            last = res;
        }
        return res;
    }

    static void Main() {
        int[] hval = { 6, 7, 1, 3, 8, 2, 4 };
        Console.WriteLine(maxLoot(hval));
    }
}
JavaScript
// Function to calculate the maximum stolen value
function maxLoot(hval) {
    const n = hval.length;

    if (n === 0)
        return 0;
    if (n === 1)
        return hval[0];

    // Set previous 2 values
    let secondLast = 0, last = hval[0];

    // Compute current value using previous two values
    // The final current value would be our result
    let res;
    for (let i = 1; i < n; i++) {
        res = Math.max(hval[i] + secondLast, last);
        secondLast = last;
        last = res;
    }
    return res;
}

const hval = [6, 7, 1, 3, 8, 2, 4];
console.log(maxLoot(hval));

Output
19

Time Complexity: O(n), Every value is computed only once.
Auxiliary Space: O(1), as we are using only two variables.


Find maximum possible stolen value - House Robber Problem
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