CSP-S1 2024 完善程序第一题。

#include <iostream>
#include <algorithm>
using namespace std;

const int maxn = 100005;

int n, m;
long long k;
int a[maxn], b[maxn];

int* upper_bound(int *a, int *an, int ai) {
	int l = 0, r = an - a;
	while (l < r) {
		int mid = (l+r)>>1;
		if (a[mid] > ai) {
			r = mid;
		} else {
			l = mid + 1;
		}
	}
	return a+l;
}

long long get_rank(int sum) {
	long long rank = 0;
	for (int i = 0; i < n; ++i) {
		rank += upper_bound(b, b+m, sum - a[i]) - b;
	}
	return rank;
}

int solve() {
	int l = 0, r = a[n - 1] + b[m - 1];
	while (l < r) {
		int mid = ((long long)l+r)>>1;
		if (get_rank(mid) < k) {
			l = mid + 1;
		} else {
			r = mid;
		}
	}
	return l;
}

int main() {
	cin >> n >> m >> k;
	for (int i = 0; i < n; ++i) cin >> a[i];
	for (int i = 0; i < m; ++i) cin >> b[i];
	sort(a, a + n), sort(b, b + m);
	cout << solve() << endl;
}