LeetCode-73. 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?

题解：

class Solution {
  static void signToMinus(int n, int m, vector<vector<int>>& matrix, int x, int y) {
    for (int i = 0; i < m; i++) {
      if (matrix[x][i] != 0) {
        matrix[x][i] = 10000;
      }
    }
    for (int i = 0; i < n; i++) {
      if (matrix[i][y] != 0) {
        matrix[i][y] = 10000;
      }
    }
  }
  public:
    void setZeroes(vector<vector<int>>& matrix) {
      int n = matrix.size();
      int m = matrix[0].size();
      for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
          if (matrix[i][j] == 0) {
            signToMinus(n, m, matrix, i, j);
          }
        }
      }
      for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
          if (matrix[i][j] == 10000) {
            matrix[i][j] = 0;
          }
        }
      }
    }
};