Codeforces 161A Dress'em in Vests!

なんかどっちを固定するかで一度、ミスって大変だった。
O(max(n,m))かなぁ。直感的には。わからん。

#include <iostream>
#include <iomanip>

#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <numeric>
#include <algorithm>

#include <functional>
#include <cctype>

#include <complex>
#include <string>
#include <sstream>

#define pb push_back
#define all(c) c.begin(),c.end()
#define rall(c) c.rbegin(),c.rend()

#define rep(i,n) for(int i=0;i<(n);i++)
#define tr(container, it) \
    for(typeof(container.begin()) it = container.begin(); it != container.end(); ++it)
#define present(container, element) (container.find(element) != container.end())
#define cpresent(container, element) (find(all(container),element) != container.end())
#define sz(a) ((int)a.size())

typedef long long ll;
const int dx[] = {1,0,-1,0};
const int dy[] = {0,-1,0,1};
const double EPS = 1e-9;

using namespace std;

int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    int n,m,x,y;
    cin >> n >> m >> x >> y;
    vector<int> A(n);
    vector<pair<int,int> > H(n);
    vector<int> B(m);
    rep(i,n) cin >> A[i];
    rep(i,m) cin >> B[i];

    sort(all(A));
    sort(all(B));

    rep(i,n){
        H[i] = make_pair(A[i]-x,A[i]+y);
    }
    vector<pair<int,int> > out;
    int ret = 0;

    int ind = 0;
    rep(i,n){
        for(int j=ind;j<m;j++){
            if(H[i].first <= B[j] && B[j] <= H[i].second){
                out.push_back(make_pair(i+1,j+1));
                ind = j+1;
                ret++;
                break;
            }else if(H[i].second < B[j]){
                break;
            }
            ind = j+1; 
        }
    }
    cout << out.size() << endl;
    tr(out,it){
        cout << (*it).first << " " << (*it).second << endl;
    }
    return 0;
}