Maximum in a 2D matrix using Multi-threading in C++

Last Updated : 3 Feb, 2023
Given a 2-D matrix, find the element having maximum value using multi-threading. Prerequisite : Multithreading Examples : 
Input : {{1, 5, 3, 6},
         {22, 10, 4, 34},
         {4, 45, 67, 3},  
         {69, 3, 23, 3}}
Output :69

Input :{{1, 2, 3}
        {2, 4, 5}}
Output :5
A matrix can be of very large size so when it comes to traversing it, it will take lot of time. When finding the max element in a matrix, each element of the matrix is to be traversed which will take more time. So, to minimize the time taken in traversing the matrix can be avoided using multi-threading.
CPP 
// CPP code to find max in 2d
// array using multi-threading
#include <bits/stdc++.h>
using namespace std;

// declaring two thread_id variable
pthread_t thread[2];

// structure for passing arguments
typedef struct dim
{
    int s, e;
}dim;

// matrix of 4X4
int mat1[][4] = {{1, 5, 3, 6}, {22, 80, 4, 34},
            {4, 45, 67, 3}, {99, 3, 23, 3}};
int maxf[2];

// function that find max from a given array
void *max(void *size)
{
    int i, j, max;
    dim *b = (dim *)size;
    max = mat1[b -> s][0];
    
    // finding max
    for(i = b -> s; i < b -> e; i++)
    {
        for(j = 0; j < 4; j++)
        {
            if(max < mat1[i][j])
                max = mat1[i][j];
        }
    }
    
    // storing max from first half of
    // 2-d array into 0th index
    if(b -> s == 0)
        maxf[0] = max;
    
    // storing max from second half of
    // 2-d array into 1st index
    else
    maxf[1] = max;
}

// driver function
int main()
{
    int i, j;
    dim *a, *b;
    a = (dim *)malloc(sizeof(dim));
    b = (dim *)malloc(sizeof(dim));
    
    // creating thread1
    a -> s = 0; a -> e = 4/2;
    pthread_create(&thread[0], NULL,
                &max, (void *)a);
    
    b -> s = 4/2; b -> e = 4;
    
    // creating thread 2
    pthread_create(&thread[1], NULL,
                &max, (void *)b);
    
    // waiting until the completion of threads
    pthread_join(thread[0], NULL);
    pthread_join(thread[1], NULL);
    
    // printing max
    if(maxf[0] > maxf[1])
    cout << maxf[0] << endl;
    else
    cout<< maxf[1] << endl;
    
    return 0;
}
Output :
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