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73. Set Matrix Zeroes

Posted on Edited on In Disqus:
Symbols count in article: 1.6k Reading time ≈ 1 mins.

O(mn) time O(1) space

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class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        if (matrix.empty() || matrix[0].empty()) return;
        int n = matrix.size(), m = matrix[0].size();
        bool row0 = false, col0 = false; // row0和col0来标记第一行和第一列是否应该被设成0
        for (int c = 0; c < m; ++c) {
            if (matrix[0][c] == 0) {
                row0 = true;
                break;
            }
        }
        for (int r = 0; r < n; ++r) {
            if (matrix[r][0] == 0) {
                col0 = true;
                break;
            }
        }
        for (int r = 1; r < n; ++r) {
            for (int c = 1; c < m; ++c) {
                if (matrix[r][c] == 0) {
                    matrix[r][0] = matrix[0][c] = 0;
                }
            }
        }
        for (int r = 1; r < n; ++r) {
            for (int c = 1; c < m; ++c) {
                if (matrix[r][0] == 0 || matrix[0][c] == 0) {
                    matrix[r][c] = 0;
                }
            }
        }
        if (row0) {
            for (int c = 0; c < m; ++c) {
                matrix[0][c] = 0;
            }
        }
        if (col0) {
            for (int r = 0; r < n; ++r) {
                matrix[r][0] = 0;
            }
        }
    }
};
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class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        if (matrix.empty() || matrix[0].empty()) return;
        int n = matrix.size(), m = matrix[0].size();
        bool col0 = false; // col0来标记第一列是否应该被设成0
        for (int r = 0; r < n; ++r) {
            if (matrix[r][0] == 0) {
                col0 = true;
            }
            for (int c = 1; c < m; ++c) {
                if (matrix[r][c] == 0) {
                    matrix[r][0] = matrix[0][c] = 0;
                }
            }
        }
        for (int r = 1; r < n; ++r) {
            for (int c = 1; c < m; ++c) {
                if (matrix[r][0] == 0 || matrix[0][c] == 0) {
                    matrix[r][c] = 0;
                }
            }
        }
        if (matrix[0][0] == 0) {
            for (int c = 0; c < m; ++c) {
                matrix[0][c] = 0;
            }
        }
        if (col0) {
            for (int r = 0; r < n; ++r) {
                matrix[r][0] = 0;
            }
        }
    }
};