LeetCode-in-Java

1277. Count Square Submatrices with All Ones

Medium

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

public class Solution {
    public int countSquares(int[][] matrix) {
        int total = 0;
        for (int[] ints : matrix) {
            total += ints[0];
        }
        for (int i = 1; i < matrix[0].length; i++) {
            total += matrix[0][i];
        }
        for (int i = 1; i < matrix.length; i++) {
            for (int j = 1; j < matrix[0].length; j++) {
                if (matrix[i][j] == 1) {
                    matrix[i][j] =
                            Math.min(
                                            matrix[i - 1][j - 1],
                                            Math.min(matrix[i - 1][j], matrix[i][j - 1]))
                                    + 1;
                }
                total += matrix[i][j];
            }
        }
        return total;
    }
}

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