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:
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?
Solution:
Code:
public void setZeroes(int[][] matrix) { int row = matrix.length, col = matrix[0].length; int overlap1 = 1; for (int i = 0; i < row; i++){ if (matrix[i][0] == 0){ overlap1 = 0; // 记录第0列是否存在零,因为(0,0)位需要存放第0行 } for (int j = 1; j < col; j++){ if (matrix[i][j] == 0){ matrix[i][0] = 0; matrix[0][j] = 0; } } } for (int i = row-1; i >= 0; i--){ // 从后开始,因为第一排是判断的前提,先改会影响到后面的判断 for (int j = col-1; j > 0 ; j--){ if (matrix[i][0] == 0 || matrix[0][j] == 0){ matrix[i][j] = 0; } } if (overlap1 == 0){ matrix[i][0] = 0; } } }
提交情况:
这个Memory Usage有点迷,我最开始测出来都是5%左右,试了多个标答都是这个结果。于是加上了0的判断,升到了57%,正当我惊叹边界对效率的提高时,我删去了边界判断,效率却变成了70%+……尽管一直知道这个值在浮动,但这个变化也太大,着实看不懂……_(:зゝ∠)_
Runtime: 1 ms, faster than 94.83% of Java online submissions for Set Matrix Zeroes.
Memory Usage: 50.5 MB, less than 5.10% of Java online submissions for Set Matrix Zeroes.
Memory Usage: 45.2 MB, less than 57.82% of Java online submissions for Set Matrix Zeroes.
Memory Usage: 44.2 MB, less than 71.94% of Java online submissions for Set Matrix Zeroes.