The "eight queens puzzle" is the problem of placing eight chess queens on an 8×8 chessboard so that no two queens threaten each other. Thus, a solution requires that no two queens share the same row, column, or diagonal. The eight queens puzzle is an example of the more general N queens problem of placing N non-attacking queens on an N×N chessboard. (From Wikipedia - "Eight queens puzzle".)

Here you are NOT asked to solve the puzzles. Instead, you are supposed to judge whether or not a given configuration of the chessboard is a solution. To simplify the representation of a chessboard, let us assume that no two queens will be placed in the same column. Then a configuration can be represented by a simple integer sequence (Q₁, Q₂, ..., Q_N), where Q_i is the row number of the queen in the i-th column. For example, Figure 1 can be represented by (4, 6, 8, 2, 7, 1, 3, 5) and it is indeed a solution to the 8 queens puzzle; while Figure 2 can be represented by (4, 6, 7, 2, 8, 1, 9, 5, 3) and is NOT a 9 queens' solution.

Figure 1		Figure 2

Input Specification:

Each input file contains several test cases. The first line gives an integer K (1 < K <= 200). Then K lines follow, each gives a configuration in the format "N Q₁ Q₂ ... Q_N", where 4 <= N <= 1000 and it is guaranteed that 1 <= Q_i <= N for all i=1, ..., N. The numbers are separated by spaces.

Output Specification:

For each configuration, if it is a solution to the N queens problem, print "YES" in a line; or "NO" if not.

Sample Input:

4

8 4 6 8 2 7 1 3 5

9 4 6 7 2 8 1 9 5 3

6 1 5 2 6 4 3

5 1 3 5 2 4

Sample Output:

YES

NO

NO

YES

 #include<cstdio>

 #include<iostream>

 #include<algorithm>

 #include<queue>

 #include<vector>

 using namespace std;

 int num[], N, K, hashTB[];

 int main(){

     scanf("%d", &K);

     for(int i = ; i < K; i++){

         scanf("%d", &N);

         fill(hashTB, hashTB + , );

         for(int j = ; j <= N; j++){

             scanf("%d", &num[j]);

             hashTB[num[j]]++;

         }

         int tag = ;

         for(int j = ; j <= N; j++){

             if(hashTB[j] != ){

                 tag = ;

                 break;

             }

             int m = j - , n = num[j] - ;

             while(m >=  && m <= N && j >=  && j <= N){

                 if(num[m] == n){

                     tag = ;

                     break;

                 }

                 m--; n--;

             }

             m = j + ; n = num[j] + ;

             while(m >=  && m <= N && j >=  && j <= N){

                 if(num[m] == n){

                     tag = ;

                     break;

                 }

                 m++; n++;

             }

         }

         if(tag == )

             printf("NO\n");

         else printf("YES\n");

     }

     cin >> N;

     return ;

 }

总结：

1、由于已经保证了不在同一列，所以只需要检查行和斜线即可。

2、检查a、b两点间的斜线，可用abs(Xa - Xb) == abs(Ya - Yb)。