LeetCode - Set Matrix Zeroes | Darren's Blog

Given an m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
A simple improvement is to make use of two arrays of length m and n , respectively, indicating which rows and columns need to be set to 0. In this way, the space complexity is reduced to O(m+n) .
A simple improvement is to make use of two arrays of length m and n , respectively, indicating which rows and columns need to be set to 0. In this way, the space complexity is reduced to O(m+n) .
Code from http://www.programcreek.com/2012/12/leetcode-set-matrix-zeroes-java/

public void setZeroes(int[][] matrix) {
        boolean firstRowZero = false;
        boolean firstColumnZero = false;
        //set first row and column zero or not
        for(int i=0; i<matrix.length; i++){
            if(matrix[i][0] == 0){
                firstColumnZero = true;
                break;
            }
        }
        for(int i=0; i<matrix[0].length; i++){
            if(matrix[0][i] == 0){
                firstRowZero = true;
                break;
            }
        }
 
        //mark zeros on first row and column
        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;
                }
            }
        }
        //use mark to set elements
        for(int i=1; i<matrix.length; i++){
            for(int j=1; j<matrix[0].length; j++){
                if(matrix[i][0] == 0 || matrix[0][j] == 0){
                   matrix[i][j] = 0;
                }
            }
        }
        //set first column and row
        if(firstColumnZero){
            for(int i=0; i<matrix.length; i++)
                matrix[i][0] = 0;
        }
        if(firstRowZero){
            for(int i=0; i<matrix[0].length; i++)
                matrix[0][i] = 0;
        }
 
    }

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