LeetCode 73. Set Matrix Zeroes

73. Set Matrix Zeroes

Difficulty: Medium

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

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(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?

Solution

Language: Java

Time Complexity: O(mn)
Space Complexity: O(m + n) 优化方法是用行和列的第一个元素存储变零状态
Beats 15%

class Solution {
    public void setZeroes(int[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return;
        }
        Set<Integer> columnSet = new HashSet<>();
        Set<Integer> rowSet = new HashSet<>();
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0) {
                    rowSet.add(i);
                    columnSet.add(j);
                }
            }
        }
        for (int row : rowSet) {
            Arrays.fill(matrix[row], 0);
        }
        for (int col : columnSet) {
            for (int i = 0; i < matrix.length; i++) {
                matrix[i][col] = 0;
            }
        }
    }
}