N-Queens II @LeetCode

Follow up for N-Queens problem.

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

	package leetcode.combinations;
	import java.util.ArrayList;
	/**
	* Solution: I am lazy... use the same way as N-Queen I
	* @author jeffwan
	* @date Apr 7, 2014
	*/
	public class TotalNQueens {
	public int totalNQueens(int n) {
	ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
	ArrayList<Integer> cols = new ArrayList<Integer>();
	search(result, cols, n);
	System.out.println(result);
	return result.size();
	}
	private void search(ArrayList<ArrayList<Integer>> result,
	ArrayList<Integer> cols, int n) {
	if (cols.size() == n) {
	result.add(new ArrayList<Integer>(cols));
	return;
	}
	for (int col = 0; col < n; col++) {
	if (!isValid(cols, col)) {
	continue;
	}
	cols.add(col);
	search(result, cols, n);
	cols.remove(cols.size() - 1);
	}
	}
	private boolean isValid(ArrayList<Integer> cols, int col) {
	int row = cols.size();
	for (int i = 0; i < row; i++) {
	if (col == cols.get(i)) {
	return false;
	}
	if (i - cols.get(i) == row - col) {
	return false;
	}
	if (i + cols.get(i) == row + col) {
	return false;
	}
	}
	return true;
	}
	}

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