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NQueens.java
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NQueens.java
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import java.util.*;
public class Solution {
public List<String[]> result = new ArrayList<String[]>();
public List<String[]> solveNQueens(int n) {
List<Integer> array = new ArrayList<Integer>();
for (int i = 0; i < n; i++) {
array.add(i+1);
}
List<Integer> curr = new ArrayList<Integer>();
this.dfs(curr, array);
return this.result;
}
public void dfs (List<Integer> curr, List<Integer> array) {
if (array.size() == 0) {
this.result.add(this.construct(curr));
return;
}
for (int i = 0; i < array.size(); i++) {
if (this.check(curr, array.get(i)) == true) {
List<Integer> copyCurr = new ArrayList<Integer>(curr);
copyCurr.add(array.get(i));
List<Integer> arrayCopy = new ArrayList<Integer>(array);
arrayCopy.remove(i);
dfs(copyCurr, arrayCopy);
}
}
}
public boolean check (List<Integer> curr, int newValue) {
for (int i = 0; i < curr.size(); i++) {
if (Math.abs(newValue-curr.get(i)) == Math.abs(curr.size()-i)) {
return false;
}
}
return true;
}
public String[] construct (List<Integer> curr) {
String[] r = new String[curr.size()];
for (int i = 0; i < curr.size(); i++) {
StringBuilder sb = new StringBuilder(curr.size());
for (int j = 0; j < curr.size(); j++) {
if ((j + 1) == curr.get(i)) {
sb.append('Q');
} else {
sb.append('.');
}
}
r[i] = sb.toString();
}
return r;
}
public static void main (String args[]) {
Solution sol = new Solution();
int n = 2;
List<String[]> result = sol.solveNQueens(n);
for (int i = 0; i < result.size(); i++) {
for (int j = 0; j < n; j++) {
System.out.println(result.get(i)[j]);
}
}
}
}