leetcode 73 Set Matrix Zeroes
z
 2019-04-09 10:36:27  

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:

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Input: 
[
  [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: 
[
  [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(m**n) 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?
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public class zeroMatrix {
  public void setZero(int[][] matrix){
    int m = matrix.length;
    int n = matrix[0].length;
    int firstRow = 1;
    int firstColum = 1;
    for (int i=0; i<m; i++) {
      if (matrix[i][0] == 0) firstColum = 0;
    }
    for (int i=0; i<n; i++) {
      if (matrix[0][i] == 0) firstRow = 0;
    }
    for (int i=1; i<m; i++) {
      for (int j=1; j<n; j++) {
        if (matrix[i][j] == 0) {
          matrix[0][j] = 0;
          matrix[i][0] = 0;
        }
      }
    }
    for (int i=1; i<n; i++) {
      for (int j=1; j<n; j++) {
        if (matrix[0][j] == 0 || matrix[i][0] == 0) {
          matrix[i][j] = 0;
        }
      }
    }
    for (int i=0; i<m; i++) {
      if (firstColum == 0) {
        matrix[i][0] = 0;
      }
    }
    for (int i=0; i<n; i++) {
      if (firstRow == 0) {
        matrix[0][i] = 0;
      }
    }
  }
}