73. Set Matrix Zeroes (Medium)

https://leetcode.com/problems/set-matrix-zeroes/

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in-place.

Example 1:

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

Example 2:

Input: 
[
  [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]
]

Follow up:

  • A straight forward 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?

Solutions

class Solution {
    public void setZeroes(int[][] matrix) {
        if (matrix == null || matrix.length == 0) {
            return;
        }

        int tmp = 1690664872;

        int row = matrix.length;
        int col = matrix[0].length;

        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (matrix[i][j] != 0) {
                    continue;
                }

                // To reach here, matrix[i][j] is 0

                // do not turn values on same row/column to 0, it will bring in consequent
                // influence for followup processing.

                for (int x = 0; x < row; x++) {
                    // do not modify the cell if original value is 0
                    if (matrix[x][j] == 0) {
                        continue;
                    }
                    matrix[x][j] = tmp;
                }

                for (int y = 0; y < col; y++) {
                    // do not modify the cell if original value is 0
                    if (matrix[i][y] == 0) {
                        continue;
                    }
                    matrix[i][y] = tmp;
                }
            }
        }

        // reset the turned values to 0
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (matrix[i][j] == tmp) {
                    matrix[i][j] = 0;
                }
            }
        }
    }
}

Incorrect Solutions

References

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