# Find Smallest Common Element in All Rows in C++

C++Server Side ProgrammingProgramming

Suppose we have a matrix mat where every row is sorted in non-decreasing order, we have to find the smallest common element in all rows. If there is no common element, then return -1. So if the matrix is like −

 1 2 3 4 5 2 4 5 8 10 3 5 7 9 11 1 3 5 7 9

The output will be 5

To solve this, we will follow these steps −

• Define a map m, n := row count of matrix,

• if n is not 0, then x = column size, otherwise 0

• for i in range 0 to n – 1

• for j in range 0 to x – 1

• if m[mat[i, j]] + 1 = i + 1, then increase m[mat[i, j]] by 1

• for each key-value pair i

• if value of i is n, then return the key of i

• return -1

## Example (C++)

Let us see the following implementation to get a better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int smallestCommonElement(vector<vector<int>>& mat) {
map <int, int> m;
int n = mat.size();
int x = n? mat[0].size() : 0;
for(int i = 0; i < n; i++){
for(int j = 0; j < x; j++){
if(m[mat[i][j]] + 1 == i + 1){
m[mat[i][j]]++;
}
}
}
map <int, int> :: iterator it = m.begin();
while(it != m.end()){
if(it->second == n){
return it->first;
}
it++;
}
return -1;
}
};
main(){
vector<vector<int>> v = {{1,2,3,4,5},{2,4,5,8,10},{3,5,7,9,11},{1,3,5,7,9}};
Solution ob;
cout << (ob.smallestCommonElement(v));
}

## Input

[[1,2,3,4,5],[2,4,5,8,10],[3,5,7,9,11],[1,3,5,7,9]]

## Output

5
Published on 31-Mar-2020 09:11:38