wayetan
12/30/2013 - 12:49 AM

## Set Matrix Zeroes

Set Matrix Zeroes

``````/**
* Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
* 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) {
boolean frtRow = false, frtCol = false;
int rows = matrix.length;
int cols = matrix[0].length;
// first make sure if the first row and first column need to be set 0 or not.
for(int i = 0; i < rows; i++){
if(matrix[i][0] == 0){
frtCol = true;
break;
}
}
for(int i = 0; i < cols; i++){
if(matrix[0][i] == 0){
frtRow = true;
break;
}
}
// scan the rest of the matrix, and mark the first row and first column in the matrix with 0s.
for(int i = 1; i < rows; i++){
for(int j = 1; j < cols; j++){
if(matrix[i][j] == 0){
matrix[i][0] = 0;
matrix[0][j] = 0;
}
}
}
// set 0s.
for(int i = 1; i < rows; i++){
for(int j = 1; j < cols; j++){
if(matrix[i][0] == 0 || matrix[0][j] == 0)
matrix[i][j] = 0;
}
}
if(frtRow){
for(int i = 0; i< cols; i++){
matrix[0][i] = 0;
}
}
if(frtCol){
for(int i = 0; i< rows; i++){
matrix[i][0] = 0;
}
}
}
}``````