二分法

复杂度: $O(nlogn)$

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

const int N = 1e6+50;
int a[N], b[N];
int n, m, k;
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];

    for(int i = 0; i < n; i++){
        int t = k - a[i];
        if(binary_search(b, b+m, t)){
            int index = lower_bound(b, b+m, t) - b;
            cout << i << " " << index << endl;
        }
    }
    return 0;
}