README.md

531. 孤独像素 I

English Version

题目描述

给你一个大小为 m x n 的图像 picture ，图像由黑白像素组成，'B' 表示黑色像素，'W' 表示白色像素，请你统计并返回图像中 黑色 孤独像素的数量。

黑色孤独像素 的定义为：如果黑色像素 'B' 所在的同一行和同一列不存在其他黑色像素，那么这个黑色像素就是黑色孤独像素。

 

示例 1：

输入：picture = [["W","W","B"],["W","B","W"],["B","W","W"]]
输出：3
解释：全部三个 'B' 都是黑色的孤独像素

示例 2：

输入：picture = [["B","B","B"],["B","B","W"],["B","B","B"]]
输出：0

 

提示：

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

解法

数组或哈希表统计每一行、每一列中 'B' 出现的次数。

Python3

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

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++

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

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
}

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