Hdu 1272 소희의 미로

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <algorithm>
using namespace std;

const int ROOM = 100010;

int p[ROOM], flag[ROOM] ;

void Init() {
    for(int i = 0; i < ROOM; i++) {
        p[i] = i;
        flag[i] = 0;
    }
}

int Find(int x) {
    while(x != p[x])
        x = p[x];
    return x;
}

void Union(int R1, int R2) {
    int r1 = Find(R1);
    int r2 = Find(R2);
    if(r1 != r2) p[r1] = r2;
}

int main() {
    int a, b;
    while(scanf("%d%d", &a, &b)!=EOF) {
        if(a == -1 || b == -1) break;
        if(a == 0 && b == 0) {
            puts("Yes");
            continue;
        }
        Init();
        int Min = ROOM, Max = -1, cnt = 0, ans = 0;
        while(a || b) {
            if(a > Max) Max = a;
            if(b > Max) Max = b;
            if(a < Min) Min = a;
            if(b < Min) Min = b;
            flag[a] = 1;
            flag[b] = 1;
            int ra = Find(a);
            int rb = Find(b);
            if(ra == rb)
                ans = 1;
            else
                Union(ra, rb);
            scanf("%d%d", &a, &b);
        }
        if(ans == 1)
            puts("No");
        else {
            for(int i = Min; i <= Max; i++) {
                if(flag[i] == 1 && p[i] == i)
                    cnt++;
            }
            if(cnt == 1) puts("Yes");
            else puts("No");
        }
    }
    return 0;
}