• leetcode : Set Matrix Zeroes [技巧 follow up 逐步优化]


    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) {
            
            		
    		if(matrix == null){
    			return;
    		}
    		
    		int m = matrix.length;
    		int n = matrix[0].length;
    		
    	    boolean row0 = false;
    	    boolean col0 = false;
    	    
    	    for(int i = 0; i < n; i++){
    	        if(matrix[0][i] == 0){
    	            row0 = true;
    	            break;
    	        }
    	    }
    	    
    	    for(int j = 0 ; j < m; j++){
    	        if(matrix[j][0] == 0){
    	            col0 = true;
    	            break;
    	        }
    	    }
    		
            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[0][j] == 0 || matrix[i][0] == 0){
                            matrix[i][j] = 0;
                        }
                    }
              
            }
            
            
            
            if(row0 == true){
                for(int i = 0; i < n; i++){
    	        matrix[0][i] = 0;
    	        }
            }
            
             if(col0 == true){
                for(int i = 0; i < m; i++){
    	        matrix[i][0] = 0;
    	        }
            }
            
        }
    }
    

      

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  • 原文地址:https://www.cnblogs.com/superzhaochao/p/6497841.html
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