My brief solution using O(m + n) space. Can someone not use extra spaces?


  • 0
    T
    public void setZeroes(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        
        boolean[] row = new boolean[m];
        boolean[] col = new boolean[n];
        
        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 < row.length; i++){
            if(row[i] == true){
                for(int j = 0; j < n; j++){
                    matrix[i][j] = 0;
                }
            }
        }
        
        for(int i = 0; i < col.length; i++){
            if(col[i] == true){
                for(int j = 0; j < m; j++){
                    matrix[j][i] = 0;
                }
            }
        }
    }

  • 0
    D

    I think the solution is obvious: use the first row & first column to mark if elements in that row/column should be 0.

    public class Solution {
        public void setZeroes(int[][] matrix) {
            
            boolean firstRowZero = false;
            boolean firstColZero = false;
            
            for(int i =0; i<matrix.length; i++)
                if(matrix[i][0] == 0) {
                    firstColZero = true;
                    break;
                }
                
            for(int i =0; i<matrix[0].length; i++)
                if(matrix[0][i] == 0) {
                    firstRowZero = true;
                    break;
                }
                    
            for(int i = 1; i<matrix.length; i++){
                for(int j = 1; j<matrix[0].length; j++){
                    if(matrix[i][j] == 0){
                        matrix[i][0] = 0;
                        matrix[0][j] = 0;
                    }
                }
            }
            
            for(int i=1; i<matrix.length; i++){
                if(matrix[i][0] == 0)
                for(int j=1; j<matrix[0].length; j++){
                    matrix[i][j] = 0;
                }
            }
            for(int i=1; i<matrix[0].length; i++){
                if(matrix[0][i] == 0)
                for(int j=1; j<matrix.length; j++){
                    matrix[j][i] = 0;
                }
            }
            
            if (firstRowZero)
                for(int i =0; i<matrix[0].length; i++)
                    matrix[0][i] = 0;
            if (firstColZero)
                for(int i=0; i<matrix.length; i++)
                    matrix[i][0] = 0;
        }
    }

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