531. Lonely Pixel I

Given an m x n picture consisting of black 'B' and white 'W' pixels, return the number of black lonely pixels.

A black lonely pixel is a character 'B' that located at a specific position where the same row and same column don't have any other black pixels.

 

Example 1:

Input: picture = [["W","W","B"],["W","B","W"],["B","W","W"]]
Output: 3
Explanation: All the three 'B's are black lonely pixels.

Example 2:

Input: picture = [["B","B","B"],["B","B","B"],["B","B","B"]]
Output: 0

 

Constraints:

  • m == picture.length
  • n == picture[i].length
  • 1 <= m, n <= 500
  • picture[i][j] is 'W' or 'B'.

Rust Solution

struct Solution;

impl Solution {
    fn find_lonely_pixel(pictures: Vec<Vec<char>>) -> i32 {
        let n = pictures.len();
        let m = pictures[0].len();
        let mut rows = vec![0; n];
        let mut cols = vec![0; m];
        for i in 0..n {
            for j in 0..m {
                if pictures[i][j] == 'B' {
                    rows[i] += 1;
                    cols[j] += 1;
                }
            }
        }
        let mut res = 0;
        for i in 0..n {
            for j in 0..m {
                if pictures[i][j] == 'B' && rows[i] == 1 && cols[j] == 1 {
                    res += 1;
                }
            }
        }
        res
    }
}

#[test]
fn test() {
    let pictures = vec_vec_char![['W', 'W', 'B'], ['W', 'B', 'W'], ['B', 'W', 'W']];
    let res = 3;
    assert_eq!(Solution::find_lonely_pixel(pictures), res);
}

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