codeforces Educational Codeforces Round 16-C

题目链接：http://codeforces.com/contest/710/problem/C

思路：刚开始没看到条件n为奇数，一上来就是DFS，搞了半天结果再怎么剪枝也是超时（显然n=2时就是无解.....）。

n是奇数就好办了，只要把奇数和偶数放在指定位置就行，答案不唯一。

#include<bits/stdc++.h>using namespace std;int a[55][55];int main(){    int n,odd=1,even=2,num=0,l,r,j;    scanf("%d",&n);    for(int i = 1 ;i <= n ;i++)    {        if(i > (n>>1) + 1) num--;        else num++;        a[i][n/2+1] = odd ,odd += 2;        for(l = n>>1 ,r = (n>>1) + 2 ,j = 2 ;j <= num ;j++ ,l-- ,r++)            a[i][l] = odd ,odd += 2 ,a[i][r] = odd ,odd += 2;        for( ;l>0;l--,r++)            a[i][l] = even ,even+=2 ,a[i][r] = even , even += 2;    }    for(int i = 1 ;i <= n ;i++)    {        for(int j = 1 ;j < n ;j++)            printf("%d ",a[i][j]);        printf("%d\n",a[i][n]);    }    return 0;}