leetcode52 N-Queens II

52. N-Queens II

Total Accepted:
41407 Total Submissions:
107148 Difficulty: Hard

Follow up for N-Queens problem.

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



AC代码：

class Solution
{
public:
int row[105];  //记录每一行皇后的位置

bool issafe(const int &i, const int &j, const int &n)
{
for (int k = 1; k < i; ++k)
if (j == row[k] || abs(i - k) == abs(j - row[k]))
return false;
return true;
}

void findPos(const int &i, const int &n, int &ans) //i表示已经放置到第i行，j表示皇后在第i行放置于j
{
for (int j = 1; j <= n; ++j)
{
if (i > n)
return;
if (issafe(i, j, n)) //判断当前位置是否可以放皇后
{
if (i == n)     //皇后已放到最后一行，找到一种解法，ans + 1
{
++ans;
continue;
}
row[i] = j;
findPos(i + 1, n, ans);
row[i] = 0;
}
}
}

int totalNQueens(int n)
{
if (1 == n)
return 1;
int ans = 0;
memset(row, 0, sizeof(row));
for (int i = 1; i <= n; ++i)   //在第一行依次放置皇后
{
row[1] = i;
findPos(2, n, ans);
}
return ans;
}
};