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?
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?
Solution1:O(mn)+ O(m+n) space
public class Solution {
public void setZeroes(int[][] matrix) {
if(matrix == null || matrix.length ==0 || matrix[0].length == 0)
return;
boolean row[] = new boolean[matrix.length];
boolean column[] = new boolean[matrix[0].length];
for(int i=0; i< row.length;i++){
for(int j=0; j< column.length; j++){
if(matrix[i][j] ==0){
row[i] = true;
column[j] = true;
}
}
}
for(int i=0; i< row.length;i++){
for(int j=0; j< column.length; j++){
if(row[i] || column[j]){
matrix[i][j] =0;
}
}
}
}
}
Solution2 :O(m*n),
public class Solution {
public void setZeroes(int[][] matrix) {
boolean firstRow=false;
boolean firstColumn=false;
for(int i=0;i<matrix.length;i++){
if(matrix[i][0]==0){
firstColumn = true;
break;
}
}
for(int i=0;i<matrix[0].length;i++){
if(matrix[0][i]==0){
firstRow = 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++){
for(int j=1;j<matrix[0].length;j++){
if(matrix[i][0]==0||matrix[0][j]==0){
matrix[i][j]=0;
}
}
}
if(firstRow){
for(int i=0;i<matrix[0].length;i++)
matrix[0][i]=0;
}
if(firstColumn){
for(int i=0;i<matrix.length;i++)
matrix[i][0]=0;
}
}
}
Key concept:use first row and column to hold the entire value
沒有留言:
張貼留言