Set Matrix Zeroes

最新推荐文章于 2020-02-14 21:39:11 发布

原创最新推荐文章于 2020-02-14 21:39:11 发布 · 537 阅读

0 ·

CC 4.0 BY-SA版权

Other Algorithms 同时被 2 个专栏收录

66 篇文章

订阅专栏

Easy

60 篇文章

订阅专栏

本文介绍了一种高效的算法，用于处理给定的m x n矩阵：当矩阵中某个元素为0时，将其所在行和列的所有元素置为0。该算法通过使用额外的布尔变量标记首行和首列是否需要置零，避免了使用额外的空间，实现了常数空间复杂度。

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

Follow up:

Did you use extra space?
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?

public class Solution {
    public void setZeroes(int[][] matrix) {
		// Start typing your Java solution below
		// DO NOT write main() function
		int m =  matrix.length;
		if(m == 0)
			return;
		int n = matrix[0].length;
		if(n == 0)
			return;
		boolean row0 = false;
		boolean col0 = false;
		for(int i = 0; i < m; i++){
			if(matrix[i][0] == 0)
				col0 = true;
		}
		for(int j = 0; j < n; j++){
			if(matrix[0][j] == 0)
				row0 = true;
		}
		for(int i = 1; i < m; i++){
			for(int j = 1; j < n; j++){
				if(matrix[i][j] == 0){
					matrix[i][0] = 0;
					matrix[0][j] = 0;
				}
			}
		}
		for(int i = 1; i < m; i++){
			for(int j = 1; j < n; j++){
				if(matrix[i][0] == 0 || matrix[0][j] == 0)
					matrix[i][j] = 0;
			}
		}
		if(col0){
			for(int i = 0; i < m; i++)
				matrix[i][0] = 0;
		}
		if(row0){
			for(int j = 0; j < n; j++)
				matrix[0][j] = 0;
		}
	}
}