[Leetcode] 52. N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

public class Solution {
private int result;
public int totalNQueens(int n) {
result = 0;
if(n <= 0) return result;
int[] columns = new int
;
helper(n, columns, 0);
return result;
}
private void helper(int n, int[] columns, int row){
if(row == n){
result++;
return;
}
for(int i = 0; i < n; i++){
if(isValid(columns, row, i)){
columns[row] = i;
helper(n, columns, row + 1);
}
}
}
private boolean isValid(int[] columns, int row1, int column1){
for(int row2 = 0; row2 < row1; row2++){
if(columns[row2] == column1) return false;
int diff = Math.abs(column1 - columns[row2]);
if(diff == (row1 - row2)) return false;
}
return true;
}
}