Graph Theory HDU

Little Q loves playing with different kinds of graphs very much. One day he thought about an interesting category of graphs called ``Cool Graph'', which are generated in the following way:
Let the set of vertices be {1, 2, 3, ..., nn}. You have to consider every vertice from left to right (i.e. from vertice 2 to nn). At vertice ii, you must make one of the following two decisions:
(1) Add edges between this vertex and all the previous vertices (i.e. from vertex 1 to i−1i−1).
(2) Not add any edge between this vertex and any of the previous vertices.
In the mathematical discipline of graph theory, a matching in a graph is a set of edges without common vertices. A perfect matching is a matching that each vertice is covered by an edge in the set.
Now Little Q is interested in checking whether a ''Cool Graph'' has perfect matching. Please write a program to help him.
Input
The first line of the input contains an integer T(1≤T≤50)T(1≤T≤50), denoting the number of test cases.
In each test case, there is an integer n(2≤n≤100000)n(2≤n≤100000) in the first line, denoting the number of vertices of the graph.
The following line contains n−1n−1 integers a2,a3,...,an(1≤ai≤2)a2,a3,...,an(1≤ai≤2), denoting the decision on each vertice.
Output
For each test case, output a string in the first line. If the graph has perfect matching, output ''Yes'', otherwise output ''No''.
Sample Input
3
2
1
2
2
4
1 1 2
Sample Output
Yes
No

No

题意：输入N组数据，每组数据输入一个n，接下来输入n-1个数，如果输入的是1，证明它可以和前面的任意一个节点相连，如果输入的是2，则不能和前面的节点相连。

判断能不能构成完美匹配。

完美匹配：如果一个图的某个匹配中，所有的顶点都是匹配点，那么它就是一个完美匹配。

#include<stdio.h>int main(){    int t;    scanf("%d",&t);    while(t--)    {        int sum=0;        int n,res[100010];        scanf("%d",&n);        for(int i=1; i<n; i++)            scanf("%d",&res[i]);        for(int i=1; i<n; i++)        {            if(i>sum && res[i]==1)                sum+=2;        }        if(!(n%2) && sum==n)            printf("Yes\n");        else            printf("No\n");    }    return 0;}//res[i]=2表示的是和前面的节点不相交，但是可以和后面res[i]=1的节点相交