Leetcode: N-Queens II

Follow up for N-Queens problem.

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

Understand the problem:
This is an extension of the N-Queen I problem, but just asks for returning the number of solutions. 

Solution:

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public class Solution {     private int result = 0;     public int totalNQueens(int n) {         if (n == 0 || n == 2 || n == 3) {             return 0;         }         int[] cols = new int[n];         totalNQueensHelper(n, 0, cols);                   return result;     }           private void totalNQueensHelper(int n, int row, int[] cols) {         if (row == n) {             result++;             return;         }                   for (int j = 0; j < n; j++) {             if (isValid(j, row, cols)) {                 cols[row] = j;                 totalNQueensHelper(n, row + 1, cols);             }         }     }           private boolean isValid(int col, int rows, int[] cols) {         for (int i = 0; i < rows; i++) {             if (cols[i] == col || rows - i == Math.abs(cols[i] - col)) {                 return false;             }         }         return true;     } }