lintcode-medium-Set Matrix Zeroes

Posted 2020-07-05 哥布林工程师

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

 

Example

Given a matrix

[
  [1,2],
  [0,3]
],

return
[
[0,2],
[0,0]
]

Challenge

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 {
    /**
     * @param matrix: A list of lists of integers
     * @return: Void
     */
    public void setZeroes(int[][] matrix) {
        // write your code here
        
        if(matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0)
            return;
        
        int m = matrix.length;
        int n = matrix[0].length;
        
        boolean first_col = false;
        boolean first_row = false;
        
        for(int i = 0; i < m; i++)
            if(matrix[i][0] == 0){
                first_col = true;
                break;
            }
        
        for(int i = 0; i < n; i++)
            if(matrix[0][i] == 0){
                first_row = 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 < n; i++){
            if(matrix[0][i] == 0){
                for(int j = 0; j < m; j++)
                    matrix[j][i] = 0;
            }
        }
        
        for(int i = 1; i < m; i++){
            if(matrix[i][0] == 0){
                for(int j = 0; j < n; j++)
                    matrix[i][j] = 0;
            }
        }
        
        if(first_col){
            for(int i = 0; i < m; i++)
                matrix[i][0] = 0;
        }
        
        if(first_row){
            for(int i = 0; i < n; i++)
                matrix[0][i] = 0;
        }
        
        return;
    }
}