题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=42
题目分析：
要能一笔画化成需要同时满足两个以下条件：
1）该图是连通的。
2）图中奇点的个数是2或者0。
参考代码：
#include<stdio.h>
#include<string.h>int set[1001];int find(int k)
{int r = set[k];while(r != set[r])r = set[r];return r;
}void merge(int r1, int r2)
{if(r1 < r2)set[r2] = r1;elseset[r1] = r2;
}int main()
{bool used[1001];int count[1001];int t,i;int a,b,c;int p,q;int r1,r2;int ans;scanf("%d", &t);while(t--){memset(count, 0, sizeof(count));memset(used, 0, sizeof(used));scanf("%d %d", &p, &q);for(i = 0; i <= q; ++i)set[i] = i;c = 0;for(i = 0; i < q; ++i){scanf("%d %d", &a, &b);if(!used[a]){++c;used[a] = true;}if(!used[b]){++c;used[b] = true;}r1 = find(a);r2 = find(b);if(r1 != r2){merge(r1,r2);--c;}++count[a];++count[b];}ans = 0;for(i = 1; i <= p; ++i){if(!used[i])++c;if(count[i] & 1)++ans;}if(c <= 1 && (ans == 2 || ans == 0))printf("Yes\n");elseprintf("No\n"); }
}
