531. Lonely Pixel I

Description

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","W"],["B","B","B"]]
Output: 0

 

Constraints:

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

Solutions

Solution 1

Python Code
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class Solution:
    def findLonelyPixel(self, picture: List[List[str]]) -> int:
        m, n = len(picture), len(picture[0])
        rows, cols = [0] * m, [0] * n
        for i in range(m):
            for j in range(n):
                if picture[i][j] == 'B':
                    rows[i] += 1
                    cols[j] += 1
        res = 0
        for i in range(m):
            if rows[i] == 1:
                for j in range(n):
                    if picture[i][j] == 'B' and cols[j] == 1:
                        res += 1
                        break
        return res

Java Code
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class Solution {
    public int findLonelyPixel(char[][] picture) {
        int m = picture.length, n = picture[0].length;
        int[] rows = new int[m];
        int[] cols = new int[n];
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (picture[i][j] == 'B') {
                    ++rows[i];
                    ++cols[j];
                }
            }
        }
        int res = 0;
        for (int i = 0; i < m; ++i) {
            if (rows[i] == 1) {
                for (int j = 0; j < n; ++j) {
                    if (picture[i][j] == 'B' && cols[j] == 1) {
                        ++res;
                        break;
                    }
                }
            }
        }
        return res;
    }
}

C++ Code
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class Solution {
public:
    int findLonelyPixel(vector<vector<char>>& picture) {
        int m = picture.size(), n = picture[0].size();
        vector<int> rows(m);
        vector<int> cols(n);
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (picture[i][j] == 'B') {
                    ++rows[i];
                    ++cols[j];
                }
            }
        }
        int res = 0;
        for (int i = 0; i < m; ++i) {
            if (rows[i] == 1) {
                for (int j = 0; j < n; ++j) {
                    if (picture[i][j] == 'B' && cols[j] == 1) {
                        ++res;
                        break;
                    }
                }
            }
        }
        return res;
    }
};

Go Code
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func findLonelyPixel(picture [][]byte) int {
	m, n := len(picture), len(picture[0])
	rows := make([]int, m)
	cols := make([]int, n)
	for i := 0; i < m; i++ {
		for j := 0; j < n; j++ {
			if picture[i][j] == 'B' {
				rows[i]++
				cols[j]++
			}
		}
	}
	res := 0
	for i := 0; i < m; i++ {
		if rows[i] == 1 {
			for j := 0; j < n; j++ {
				if picture[i][j] == 'B' && cols[j] == 1 {
					res++
					break
				}
			}
		}
	}
	return res
}