73. Set Matrix Zeroes

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73. Set Matrix Zeroes

Description

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0‘s.

You must do it in place.

Example 1:

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Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]
Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

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Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

Constraints:

  • m == matrix.length
  • n == matrix[0].length
  • 1 <= m, n <= 200
  • -2^31 <= matrix[i][j] <= 2^31 - 1

Follow up:

  • A straightforward solution using O(mn) space is probably a bad idea.
  • A simple improvement uses O(m + n) space, but still not the best solution.
  • Could you devise a constant space solution?

Hints/Notes

  • 2024/12/22
  • No solution from 0x3F

Solution

Language: C++

Constant extra space

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class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        bool col0 = false;
        int m = matrix.size(), n = matrix[0].size();
        for (int i = 0; i < m; i++) {
            if (!matrix[i][0]) col0 = true;
            for (int j = 1; j < n; j++) {
                if (!matrix[i][j]) {
                    matrix[i][0] = matrix[0][j] = 0;
                }
            }
        }
        for (int i = m - 1; i >= 0; i--) {
            for (int j = n - 1; j >= 1; j--) {
                if (!matrix[i][0] || !matrix[0][j]) {
                    matrix[i][j] = 0;
                }
            }
            if (col0) matrix[i][0] = 0;
        }
    }
};
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class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        int m = matrix.size(), n = matrix[0].size();
        vector<int> rows(m, 0), cols(n, 0);
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == 0) {
                    rows[i] = 1;
                    cols[j] = 1;
                }
            }
        }
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (rows[i] || cols[j]) {
                    matrix[i][j] = 0;
                }
            }
        }
    }
};