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MAY-21 2020 Challenge

Count Square Submatrices with All Ones


Given a m * n matrix of ones and zeros, return how many square submatrices have all ones.

Example 1:
Input: matrix =
[
  [0,1,1,1],
  [1,1,1,1],
  [0,1,1,1]
]
Output: 15
Explanation: 
There are 10 squares of side 1.
There are 4 squares of side 2.
There is  1 square of side 3.
Total number of squares = 10 + 4 + 1 = 15.
Example 2:
Input: matrix = 
[
  [1,0,1],
  [1,1,0],
  [1,1,0]
]
Output: 7
Explanation: 
There are 6 squares of side 1.  
There is 1 square of side 2. 
Total number of squares = 6 + 1 = 7.

Constraints:


1 <= arr.length <= 300
1 <= arr[0].length <= 300
0 <= arr[i][j] <= 1

Solution in C++

class Solution {
public:
    int n,m,cnt=0;
    int mat[302][302],dp[302][302];
    int  dfs(int i,int j)
    {
        if(i>=n||j>=m)
            return 0;
        if(mat[i][j]==0)
            return 0;
        if(dp[i][j]!=-1)
            return dp[i][j];
        int p=dfs(i+1,j);
        int q=dfs(i,j+1);
        int r=dfs(i+1,j+1);
        return dp[i][j]=1+min(p,min(q,r));
    }
    int countSquares(vector<vector<int>>& matrix) {
        int ans=0;
        for(int i=0;i<matrix.size();i++)
        {
            
            for(int j=0;j<matrix[i].size();j++)
            {
               mat[i][j]=matrix[i][j];
            }
        }
        memset(dp,-1,sizeof(dp));
        n=matrix.size();
        m=matrix[0].size();
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(mat[i][j]==1)
                {
                   ans+= dfs(i,j);
                }}}
        return ans;
    }};


Leetcode May 21


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