IndiaHacks 2016 - Online Edition (Div. 1 + Div. 2)-C - Bear and Up-Down-暴力枚举

http://codeforces.com/contest/653/problem/C

题意：

给n,给n个数。

要求一个合法序列满足： 偶数项>奇数项，奇数项<偶数项

给一个序列，要求交换仅一对数，使得原序列变成合法序列

问你有多少种方案

扫一遍 看有多少个位置不符合要求，也就是  偶数项《奇数项，奇数项》偶数项的，我们把后一项坐标记录起来。

如果这样的坐标如果超过2个，显然无法一次交换解决。

如果flag==1，则 枚举 x，和x-1 能和谁交换，注意 与自己相邻的坐标交换要注意左右会变化

如果flag==2，则枚举 x-1，x 和 y,y-1分别交换的四种情况，注意 与自己相邻的坐标交换要注意左右会变化

然后就完了。。。。代码写得太挫了、、、

#include <cstdio>#include <cmath>#include <cstring>#include <string>#include <algorithm>#include <queue>#include <map>#include <set>#include <vector>#include <iostream>using namespace std;const double pi=acos(-1.0); double eps=0.000001; int min(int a,int b){return a<b?a:b;} int max(int a,int b){return a>b?a:b;}int tm[150005];int wa[150005];int main(){int i,j;int n;cin>>n;for (i=1;i<=n;i++)scanf("%d",&tm[i]);if (n%2) tm[n+1]=150005;else tm[n+1]=0;tm[0]=150005;int flag=0;for (i=2;i<=n;i++){if (i%2){if (tm[i]>=tm[i-1]) {wa[++flag]=i;i++;}}else{if (tm[i]<=tm[i-1]) {wa[++flag]=i;i++;}}}if (flag>2) {printf("0\n");return 0;}if (flag==1){int sum=0;for (int k=1;k<=2;k++)for (i=1;i<=n;i++){int x;if (k==1) x=wa[1];elsex=wa[1]-1;if (i==x) continue;if (k==2) {if (x%2){if (tm[x+1]<tm[x+2]) break;}else{if (tm[x+1]>tm[x+2]) break;}}if (i==x+1&&k==1)  {if (x%2==0){if (tm[i]>tm[x]&&tm[i]>tm[x-1])if (tm[x]<tm[i]&&tm[x]<tm[i+1])sum++;}else{if (tm[i]<tm[x]&&tm[i]<tm[x-1])if (tm[x]>tm[i]&&tm[x]>tm[i+1])sum++;}}if (i==x-1){if (x%2==0){if (tm[i]>tm[x]&&tm[i]>tm[x+1])if (tm[x]<tm[i]&&tm[x]<tm[i-1])sum++;}else{if (tm[i]<tm[x]&&tm[i]<tm[x+1])if (tm[x]>tm[i]&&tm[x]>tm[i-1])sum++;}}elseif (i%2){if (tm[x]<tm[i-1]&&tm[x]<tm[i+1]){if (x%2){if (tm[i]<tm[x-1]&&tm[i]<tm[x+1])sum++;}else{if (tm[i]>tm[x-1]&&tm[i]>tm[x+1])sum++;}}}else{if (tm[x]>tm[i-1]&&tm[x]>tm[i+1]){if (x%2){if (tm[i]<tm[x-1]&&tm[i]<tm[x+1])sum++;}else{if (tm[i]>tm[x-1]&&tm[i]>tm[x+1])sum++;}} }}printf("%d\n",sum); return 0;}    //swap(wa[1],wa[2]);int sum=0;int x1=wa[1];int x2=wa[2];for (i=1;i<=4;i++){if (i==2){x1=wa[1]-1; x2=wa[2];}if (i==3) {x1=wa[1];x2=wa[2]-1;}if (i==4) {x1=wa[1]-1;x2=wa[2]-1;}if (x1>x2) swap(x1,x2);if (x1==x2-1){if (x2%2==0){if (tm[x1]>tm[x2]&&tm[x1]>tm[x2+1])if (tm[x2]<tm[x1]&&tm[x2]<tm[x1-1])sum++;}else{if (tm[x1]<tm[x2]&&tm[x1]<tm[x2+1])if (tm[x2]>tm[x1]&&tm[x2]>tm[x1-1])sum++;}}if (x1%2) if (tm[x2]<tm[x1-1]&&tm[x2]<tm[x1+1]) {if (x2%2&&tm[x1]<tm[x2-1]&&tm[x1]<tm[x2+1])sum++; if (x2%2==0&&tm[x1]>tm[x2-1]&&tm[x1]>tm[x2+1]) sum++;}if (x1%2==0)if (tm[x2]>tm[x1-1]&&tm[x2]>tm[x1+1]){if (x2%2&&tm[x1]<tm[x2-1]&&tm[x1]<tm[x2+1])sum++; if (x2%2==0&&tm[x1]>tm[x2-1]&&tm[x1]>tm[x2+1]) sum++;}}printf("%d\n",sum);return 0;}