[LeetCode 73] Set Matrix Zeroes

题目链接：set-matrix-zeroes

import java.util.Arrays;

/**
 * 
		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 SetMatrixZeroes {

	//解法一
//	157 / 157 test cases passed.
//	Status: Accepted
//	Runtime: 273 ms
//	Submitted: 0 minutes ago
	//时间复杂度O(mn) 空间复杂度O(1)
	
	//复用第0行和第0列，用来标记某列和某行是否该置0
    public void setZeroes(int[][] matrix) {
    	 int m = matrix.length;
         int n =matrix[0].length;
         boolean row0 = false;		//先标记第0行是否包含0
         boolean col0 = false;		//先标记第0列是否包含0
         for(int i = 0; i < m; i++) {
        	 if(matrix[i][0] == 0) {
        		 col0 = true;
        		 break;
        	 }
         }
         for(int i = 0; i < n; i++) {
        	 if(matrix[0][i] == 0) {
        		 row0 = true;
        		 break;
        	 }
         }
         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 < m; i++) {
 			for (int j = 1; j < n; j++) {
 				if(matrix[0][j] == 0 || matrix[i][0] == 0 ) {
 					matrix[i][j] = 0;
 				}
 			}
 		}
        if(col0) {
        	for(int i = 0; i < m; i++) {
        		matrix[i][0] = 0;
            }
        }
        if(row0) {
        	for(int i = 0; i < n; i++) {
        		matrix[0][i] = 0;
            }
        }
    }
	
	//第二种解法
//	157 / 157 test cases passed.
//	Status: Accepted
//	Runtime: 365 ms
//	Submitted: 0 minutes ago
	//时间复杂度O(mn) 空间复杂度O(m+n)
    public void setZeroes1(int[][] matrix) {
        int m = matrix.length;
        int n =matrix[0].length;
        boolean[] row = new boolean[m];
        boolean[] col = new boolean[n];
        Arrays.fill(row, false);
        Arrays.fill(col, false);
        
        for (int i = 0; i < m; i++) {
			for (int j = 0; j < n; j++) {
				if(matrix[i][j] == 0) {
					row[i] = true;
					col[j] = true;
				}
			}
		}
        for (int i = 0; i < m; i++) {
			for (int j = 0; j < n; j++) {
				if(row[i] || col[j] ) {
					matrix[i][j] = 0;
				}
			}
		}
    }
	public static void main(String[] args) {
		// TODO Auto-generated method stub

	}

}

[LeetCode 73] Set Matrix Zeroes

原文：http://blog.csdn.net/ever223/article/details/44603075