Maximum Consecutive Increasing Path Length in Binary Tree in C++

Suppose we have a binary tree; we have to calculate the length of the longest path which consists of nodes with consecutive values in increasing order. Every node will be treated as a path of length 1.

So, if the input is like

then the output will be 3 as (11, 12, 13) is maximum consecutive path.

To solve this, we will follow these steps −

• Define a function solve(), this will take root, prev_data, prev_length,
• if not root is non-zero, then −
  • return prev_length
• cur_data := val of root
• if cur_data is same as prev_data + 1, then −
  • return maximum of solve(left of root, cur_data, prev_length+1) and solve(right of root, cur_data, prev_length+1)
• newPathLen := maximum of solve(left of root, cur_data, 1) and solve(right of root, cur_data, 1)
• return maximum of prev_length and newPathLen
• From the main method do the following −
• if root is same as NULL, then −
  • return 0
• return solve(root, val of root-1, 0)

Example (C++)

Let us see the following implementation to get better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class TreeNode {
   public:
      int val;
      TreeNode *left, *right;
      TreeNode(int data) {
         val = data;
         left = NULL;
         right = NULL;
      }
};
int solve(TreeNode *root, int prev_data, int prev_length){
   if (!root)
      return prev_length;
   int cur_data = root->val;
   if (cur_data == prev_data+1){
      return max(solve(root->left, cur_data, prev_length+1), solve(root->right, cur_data, prev_length+1));
   }
   int newPathLen = max(solve(root->left, cur_data, 1), solve(root->right, cur_data, 1));
   return max(prev_length, newPathLen);
}
int maxLen(TreeNode *root){
   if (root == NULL)
      return 0;
   return solve(root, root->val-1, 0);
}
int main(){
   TreeNode *root = new TreeNode(10);
   root->left = new TreeNode(11);
   root->right = new TreeNode(9);
   root->left->left = new TreeNode(13);
   root->left->right = new TreeNode(12);
   root->right->left = new TreeNode(13);
   root->right->right = new TreeNode(8);
   cout << maxLen(root);
   return 0;
}

Input

TreeNode *root = new TreeNode(10);
root->left = new TreeNode(11);
root->right = new TreeNode(9);
root->left->left = new TreeNode(13);
root->left->right = new TreeNode(12);
root->right->left = new TreeNode(13);
root->right->right = new TreeNode(8);

Output

3