gistfile1.cpp

#include <cstdio>
// #include <unordered_map>
#include <algorithm>
#include <vector>

char _getchar()
{
    static char buf[1000000], *p1 = buf, *p2 = buf;
    return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1000000, stdin), p1 == p2) ? EOF : *p1++;
}

void get_int(int* u)
{
    static char c;
    while ((c = _getchar()) < '0') if (c == EOF) return;
    *u = c - '0';
    while ((c = _getchar()) >= '0') *u = (*u << 3) + (*u << 1) + (c ^ '0');
}

int count[100001] = { 0 };
int main()
{
    int n, m;

    get_int(&n);
    int stones[n], max = -1;
    for (int i = 0; i < n; ++i) {
        get_int(&stones[i]);
        ++count[stones[i]];
        if (stones[i] > max) max = stones[i];
    }
    max *= 2;
    std::sort(stones, stones + n);
    std::vector<int> stones_unique;
    int pre_value = -1;
    for(int i=0;i<n;i++){
        if(stones[i]!=pre_value) {
            stones_unique.push_back(stones[i]);
            pre_value = stones[i];
        }
    }

    get_int(&m);
    do {
        int sum;
        get_int(&sum);
        if (sum > max) {
            printf("0 ");
            continue;
        }

        long long answer = 0;
        for (int i = 0; i < stones_unique.size(); ++i) {
            if(stones_unique[i] > sum/2) break;
            int complement = sum - stones_unique[i];
            // if(complement < 0) break;
            if(complement == stones_unique[i])  // C(n, 2)
                answer += (count[complement] * (count[complement] - 1))/2;
            else    // C(n, 1) * C(m, 1)
                answer += count[stones_unique[i]] * count[complement];
        }
        printf("%lld ", answer );
    } while(--m);
    return 0;
}