# My Easy Understand Java Solution

• ``````public class Solution {

private final Set<Integer> cols = new HashSet<Integer>();
private final Set<Integer> diag1s = new HashSet<Integer>();
private final Set<Integer> diag2s = new HashSet<Integer>();
List<List<String>> re = new ArrayList<List<String>>();
public List<List<String>> solveNQueens(int n) {
int[][] s = new int[n][n];
helper(0,n,s);
return re;
}

private void helper(int row,int n,int[][] s){
for(int col=0;col<n;col++){
if(cols.contains(col))
continue;
int diag1 = row+col;
if(diag1s.contains(diag1))
continue;
int diag2 = row-col;
if(diag2s.contains(diag2))
continue;
if(row==n-1){
s[row][col] = 1;
s[row][col] = 0;
}else{
s[row][col] = 1;
helper(row+1,n,s);
s[row][col] = 0;
cols.remove(col);
diag1s.remove(diag1);
diag2s.remove(diag2);
}
}

}

private List<String> convertToList(int[][] s,int n){
List<String> solution = new ArrayList<String>();
for(int i=0;i<n;i++){
StringBuilder line = new StringBuilder();
for(int j=0;j<n;j++){
if(s[i][j]==0){
line.append(".");
}else{
line.append("Q");
}
}