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NQueens.java
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NQueens.java
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package src.java.hard.backtracking;
import java.util.ArrayList;
import java.util.List;
public class NQueens {
public List<List<String>> solveNQueens(int n) {
int[] num = new int[n];
List<List<String>> ret = new ArrayList<>();
solveNQueens(0, num, ret);
return ret;
}
public void solveNQueens(int n, int[] num, List<List<String>> ret){
if (n==num.length){
ret.add(convert(num));
return;
}
for (int i=0; i<num.length; i++){
num[n] = i;
if (validate(n, num))
solveNQueens(n+1, num, ret);
}
}
public boolean validate(int n, int[] num){
for (int i=0; i<n; i++){
if (num[i]==num[n] || Math.abs(num[n]-num[i])==n-i)
return false;
}
return true;
}
public List<String> convert(int[] n){
List<String> ret = new ArrayList<>();
for (int i=0; i<n.length; i++){
StringBuilder str = new StringBuilder();
for (int j=0; j<n.length; j++){
if (n[i]==j)
str.append('Q');
else
str.append('.');
}
ret.add(str.toString());
}
return ret;
}
}