(Java)LeetCode-52. N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.



这一题和上一题一样嘛。。代码几乎一模一样，就是返回原来的List的Size而已~代码如下：

public class Solution {
public int totalNQueens(int n) {

List<List<String>> result = new ArrayList<List<String>>();
List<String> line = new ArrayList<String>();
char[][] cube = new char

;
for(int i = 0; i < cube.length; i++){
for(int j = 0; j < cube[i].length; j++){
cube[i][j] = '.';
}
}
boolean[] flags = new boolean
;
solveNQueens(result, cube, flags, n, 0);
return result.size();

}

private void solveNQueens(List<List<String>> result, char[][] cube,boolean[] flags,int n, int cnt) {
// TODO Auto-generated method stub
if(cnt == n){
List<String> list = new ArrayList<String>();
for(char[] ch : cube){
list.add(new String(ch));
}
result.add(list);
return ;
}
for(int i = 0; i < flags.length; i++){
if(flags[i] == false){
List<Integer> temp = aPosition(cube, i);
if(temp.size() == 0){
break;
}
for(int t : temp){
cube[i][t] = 'Q';
flags[i] = true;
solveNQueens(result, cube, flags, n , cnt+1);
cube[i][t] = '.';
flags[i] = false;
}
break;
}
}
}

private List<Integer> aPosition(char[][] cube, int num) {
// TODO Auto-generated method stub
List<Integer> result = new ArrayList<Integer>();
int n = cube.length;
boolean flag = false;
for(int i = 0; i < n; i++){ //the direction is "--"
if(cube[num][i] == 'Q'){
return result;
}
}

for(int i = 0; i < n; i++){
for(int j = 0; j < n; j++){ //the direction is "|"
if(cube[j][i] == 'Q'){
flag = true;
break;
}
}
if(flag == false){
if(num >= i){ // the direction is "\"
int dif = num - i;
for(int j = 0; j + dif <= n-1; j++){
if(cube[j+dif][j] == 'Q'){
flag = true;
break;
}
}
}else{
int dif = i - num;
for(int j = 0; j + dif <= n-1; j++){
if(cube[j][j+dif] == 'Q'){
flag = true;
break;
}
}
}
if(flag == false){
if(num + i <= n-1){ //the direction is "/"
int sum = i + num;
for(int j = 0; sum >= j; j++ ){
if(cube[j][sum-j] == 'Q'){
flag = true;
break;
}
}
}else{
int sum = i + num;
for(int j = n-1; sum-j <= n-1; j--){
if(cube[sum-j][j] == 'Q'){
flag = true;
break;
}
}
}
}
}
if(flag == false){
result.add(i);
}else{
flag = false;
}
}
return result;
}

}