[LeetCode] N-Queens II

Follow up for N-Queens problem.

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



思路：与http://www.cnblogs.com/vincently/p/4714230.html思路相同。

class Solution {
public:
int result;
int queen_num_;
int totalNQueens(int n) {
result = 0;
vector<int> a(n, -1);
queen_num_ = n;
solveNQueens(a);

return result;
}

bool IsValid(const vector<int>& a, int row, int col) {
for (int i = 0; i < row; i++) {
if (col == a[i] || abs(i - row) == abs(a[i] - col))
return false;
}

return true;
}

void solveNQueens(vector<int>& a) {
int i = 0, j = 0;
while (i < queen_num_) {
while (j < queen_num_) {
if (IsValid(a, i, j)) {
a[i] = j;
j = 0;
break;
} else {
j++;
}
}

if (a[i] == -1) {
if (i == 0) {
return;
} else {
i--;
j = a[i] + 1;
a[i] = -1;
continue;
}
}

if (i == queen_num_  - 1) {
result++;
j = a[i] + 1;
a[i] = -1;
continue;
}
i++;
}//while (i < queen_num_);
}//solveNQueens
};