UVa 10763 - Foreign Exchange

来源：互联网发布：不想写作业知乎编辑：程序博客网时间：2024/06/04 17:48

题目：给你一个图的边集，问是不是多有的边都有回边。

分析：图论，排序。直接排序查找判定即可。

按照边的最小端点，和最大端点排序，则成对的边（或者相同的边）一定相邻。

说明：(⊙_⊙)。

#include <algorithm>#include <iostream>#include <cstdlib>#include <cstring>#include <cstdio>#include <cmath>using namespace std;typedef struct snode{int a,b,l,r;}student;student S[500001];int     U[500001];int cmp(student p, student q){if (p.l == q.l)return p.r < q.r;return p.l < q.l;}int main(){int n,x,y;while (~scanf("%d",&n) && n) {for (int i = 0 ; i < n ; ++ i) {scanf("%d%d",&x,&y);S[i].a = x; S[i].b = y;S[i].l = min(x, y);S[i].r = max(x, y); }  int flag = 1; if (n%2 == 0) { sort(S, S+n, cmp); memset(U, 0, sizeof(U)); for (int k,j,i = 0 ; i < n ; ++ i) if (!U[i]) {U[i] = 1;j = i+1; k = 0;while (S[j].l == S[i].l && S[j].r == S[i].r) { if (!U[j] && S[i].a == S[j].b && S[i].b == S[j].a) {U[j] = 1; k = 1; break;}j ++;}if (!k) { flag = 0; break;}}}else flag = 0;if (flag) printf("YES\n");else printf("NO\n");}    return 0;}

0 0