Leetcode(73) Set Matrix Zeroes

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Description

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(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?

解法

题目中要求直接替换，那么为了节省空间，可以选择将需要替换的行号和列号用list存起来，然后统一进行替换。

具体代码如下：

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class Solution {
    public void setZeroes(int[][] matrix) {
        List<Integer> row = new ArrayList<>();
        List<Integer> col = new ArrayList<>();
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0) {
                    row.add(i);
                    col.add(j);
                }
            }
        }
        for (int i = 0; i < row.size(); i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                matrix[row.get(i)][j] = 0;
            }
        }
        for (int j = 0; j < col.size(); j++) {
            for (int i = 0; i < matrix.length; i++) {
                matrix[i][col.get(j)] = 0;
            }
        }
        return;
    }
}