SPOJ4580 ABCDEF(meet in the middle)

题意

题目链接

sol

发现abcdef是互不相关的

那么meet in the middle一下。先算出abc的，再算def的

注意d = 0的时候不合法(害我wa了两发。。)

#include<bits/stdc++.h>
#define ll long long 
using namespace std;
const int maxn = 101, ss = 2e6 + 10;
map<ll, ll> mp;
int n;
ll a[maxn], ans;
int a1[ss], c1, a2[ss], c2, cnt[ss];
int main() {
//  ios::sync_with_stdio(false);
    cin >> n;
    for(int i = 1; i <= n; i++) cin >> a[i];
    sort(a + 1, a + n + 1);
    for(int i = 1; i <= n; i++) 
        for(int j = 1; j <= n; j++) 
            for(int k = 1; k <= n; k++) 
                a1[++c1] = a[i] * a[j] + a[k];
    for(int i = 1; i <= n; i++) 
        for(int j = 1; j <= n; j++) 
            for(int k = 1; k <= n; k++) 
                if(a[i] != 0) a2[++c2] = a[i] * (a[j] + a[k]);
    sort(a1 + 1, a1 + c1 + 1);
    sort(a2 + 1, a2 + c2 + 1);
    for(int i = 1, j = 1; i <= c2; i++) {
        if(i != 1 && (a2[i] == a2[i - 1])) {cnt[i] = cnt[i - 1]; continue;}
        while(a1[j] <= a2[i] && j <= c1) {
            if(a1[j] == a2[i]) cnt[i]++;
            j++;
        }
    }
    for(int i = 1; i <= c2; i++) ans += cnt[i];
    cout << ans;
    return 0;
}