leetcode hard模式专杀之51. N-Queens

public class Solution {
public List<String>  transfer(int[] q){
List<String> result = new ArrayList<>();
for(int i = 0; i<q.length; i++){
StringBuilder sb = new StringBuilder();
for(int j=0; j<q.length; j++){
if(j==q[i]){
sb.append("Q");
}else{
sb.append(".");
}
}
result.add(sb.toString());
}
return result;
}
public List<List<String>> solveNQueens(int n) {
List<List<String>> result = new ArrayList<>();
int[] q=new int
;
for(int i = 0 ; i<n; i++){
enumerate(result, i, q, 0);
}

return result;
}

public boolean isConsistent(int[] q, int line, int index){
if(line==0){
return true;
}else{
for(int i=0; i<line;i++){
//i行q[i]列 vs line行index列
if(q[i]==index){
//同列
return false;
}
if(index-q[i]==line-i){
return false;
}
if(index-q[i]==i-line){
return false;
}
}
return true;
}
}

public void enumerate(List<List<String>> result, int index, int[] q, int line){
if(line==q.length-1){
if(isConsistent(q, line, index)){
q[line] = index;
result.add(transfer(q));
}
}else if(line == 0){
q[line] = index;
for(int j = 0; j<q.length; j++){
enumerate(result, j, q, line+1);
}
}else{
if(isConsistent(q, line, index)){
q[line] = index;
for(int j = 0; j<q.length; j++){
enumerate(result, j, q, line+1);
}
}
}
}
}