Leetcode: My solution N-queens

N-Queens total accepted: 15603 total submissions: 60198my submissions

The N-Queens puzzle is the problem of placing n queens on an n × n chessboard such that no two queens attack each other.

Given an integer N, return all distinct solutions to the n-Queens puzzle.

Each solution contains a distinct board configuration of the N-Queens 'placement, where‘Q‘And‘.‘Both indicate a queen and an empty space respectively.

For example,
There exist two distinct solutions to the 4-Queens puzzle:

[ [".Q..",  // Solution 1  "...Q",  "Q...",  "..Q."], ["..Q.",  // Solution 2  "Q...",  "...Q",  ".Q.."]]

public class Solution {  public List<String[]> solveNQueens(int n) {        List<String[]> result = new ArrayList<String[]>();        if ( n < 1) {            return result ;        }        List<List<Integer>> storeArray = new ArrayList<List<Integer>>();        helper(n, new ArrayList<Integer>(), storeArray);result = drawPicture(storeArray,n);        return result;    }        private List<String[]> drawPicture(List<List<Integer>> storeArray ,int n) {    List<String[]> drawedPicture = new ArrayList<String[]> ();    for (int i = 0; i < storeArray.size();i++) {    String[] str = new String[n];    for (int j = 0; j < n; j++) {        str[j] = new String("");    for (int w = 0; w < n; w++) {    if (storeArray.get(i).get(j) == w) {    str[j] +="Q";    } else {    str[j] +=".";    }    }        }    drawedPicture.add(str);    }    return drawedPicture;}boolean isValid(ArrayList<Integer> cols, int col) {       int newX = col;       int newY = cols.size();    for (int y = 0; y < cols.size(); y++) {    int x = cols.get(y);        if (newX == x) {    return false;    }    if (newX - newY == x - y) {    return false;    }    if (newX + newY == x + y){    return false;    }    }    return true;    }    public void helper(int n, ArrayList<Integer> cols,  List<List<Integer>> storeArray) {    if (cols.size() == n) {    storeArray.add(new ArrayList<Integer>(cols));    return;    }    for (int i = 0; i < n; i++) {    if (!isValid(cols, i)) {    continue;    }    cols.add(i);    helper(n, cols, storeArray);    cols.remove(cols.size() - 1);    }    }}

Leetcode: My solution N-queens