sicily 1021

好久没写C/c++了，明天有个小比赛，然后找了一道超水的题来练手，结果很悲剧。。。虽然是1AC，解题书路就是用数组模仿个链表。。。。

/*
 * =====================================================================================
 *
 *       Filename:  test.cpp
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  04/06/2012 08:09:29 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  alfredtofu (Tofu), [e-mail]
 *        Company:  
 *
 * =====================================================================================
 */
#include <iostream>
#include <string>
#include <stack>
#include <cstring>
using namespace std;

struct Pair {
    int x;
    int y;
};


int main() {
    int n;
    int a, b, c;
    int next[100002];
    cin >> n;
    while(n != 0) {
        bool ok = false;
        memset(next, -1, sizeof(next));
        stack<Pair> s; 
        for(int i = 0; i < n; i++) {
            cin >> a >> b;   
            ok = false;
            if(a > b) {
                c = a;
                a = b;
                b = c;
            }
            if(a + 1 == b) {
                next[a] = b;
                ok = true;
            } else if(next[a + 1] == b - 1){
                next[a] = b;
                ok = true;
            } 
            if(!ok) {
                Pair tmp;
                tmp.x = a;
                tmp.y = b;
                s.push(tmp);
            } else {
                Pair tmp;
                while(!s.empty()) {
                    tmp = s.top();
                    ok = false;
                    if(tmp.x + 1 == tmp.y) {
                        next[tmp.x] = tmp.y;
                        ok = true;
                    }else if(next[tmp.x + 1] == tmp.y - 1) {
                        next[tmp.x] = tmp.y;
                        ok = true;
                    }
                    if(!ok)
                        break;
                    s.pop();
                }
            }
        }
        cin >> n;
        if(s.empty())
            cout << "Yes\n";
        else cout << "No\n";
    }
    return 0;
}