Largest Point hdu 5461

http://acm.hdu.edu.cn/showproblem.php?pid=5461

分析：一开始很撒很撒的分了很多种情况去写了，后来发现可以先储存a*num*num和b*num的值，然后再判断最大值。。

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <stack>
#include <math.h>

using namespace std;

#define met(a, b) memset(a, b, sizeof(a))
const int maxn=5000007;
#define oo 0x3f3f3f3f
const int MOD = 1e9+7;

typedef long long LL;
int num[maxn];

struct node
{
    LL sum;
    int index;
}a[maxn], b[maxn];

int cmp(node p, node q)
{
    return p.sum>q.sum;
}

int main()
{
    int T, n, A, B, cnt=1;
    LL  num;

    scanf("%d", &T);

    while(T --)
    {
        scanf("%d %d %d", &n, &A, &B);

        for(int i=0; i<n; i++)
        {
            scanf("%lld", &num);
            a[i].sum=A*num*num;
            a[i].index = i;
            b[i].sum=B*num;
            b[i].index = i;
        }

        sort(a, a+n, cmp);
        sort(b, b+n, cmp);

        if(a[0].index != b[0].index)
            printf("Case #%d: %lld\n", cnt++, a[0].sum+b[0].sum);
        else
        {
            LL p = max(a[0].sum+b[1].sum, a[1].sum+b[0].sum);
            printf("Case #%d: %lld\n",cnt++, p);
        }
    }
    return 0;
}