leetcode--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.
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 {
/**The algorithm is simple. but we need to pay attention to the first row and first column.
* @author Averill Zheng
* @version 2014-06-15
* @since JDK 1.7
*/
public void setZeroes(int[][] matrix) {
int row = matrix.length;
if(row > 0){
int column = matrix[0].length;
//find if we need to set first row or first column to be zero
boolean setRow = false;
boolean setColumn = false;
for(int i = 0; i < column; ++i){
if(matrix[0][i] == 0){
setRow = true;
break;
}
}
for(int i = 0; i < row; ++i){
if(matrix[i][0] == 0){
setColumn = true;
break;
}
}
for(int i = 1; i < row; ++i){
for(int j = 1; j < column; ++j){
if(matrix[i][j] == 0){
matrix[i][0] = 0;
matrix[0][j] = 0;
}
}
}
//set zeros;
for(int j = 1; j < column; ++j){
if(matrix[0][j] == 0){
for(int i = 1; i < row; ++i)
matrix[i][j] = 0;
}
}
for(int i = 1; i < row; ++i){
if(matrix[i][0] == 0){
for(int j = 1; j < column; ++j)
matrix[i][j] = 0;
}
}
if(setRow){
for(int i = 0; i < column; ++i)
matrix[0][i] = 0;
}
if(setColumn){
for(int i = 0; i < row; ++i)
matrix[i][0] = 0;
}
}
}
}

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