我正在尝试顶点覆盖问题。即使是一个不完美的代码也清除了所有关于soj判断的案例，但是我得到了一个测试用例（在评论中），它失败了，所以我试图删除它。但是，现在它不接受。 Problem Link
问题描述：你必须找到一个有意的无向树的顶点覆盖，即在这个树中找到一个最小尺寸的顶点集，这样每个边在该集合中至少有一个端点。
我的算法基于DFS。之前我使用了一个直截了当的逻辑，即DFS和回溯时，如果不包括子顶点，则包括其父级（如果尚未包含）。而且，它被接受了。但是，它在一个简单的具有6个顶点的倾斜树的情况下失败了。答案应该是2，但是它给了3.所以，我做了一些修改。
我添加了另一个参数来检查顶点是否已被其父级或其子级覆盖，如果是，则忽略。因此，每当找到一个尚未覆盖的顶点时，我会在顶点集中添加它的父节点。
我的旧源代码：
vector<int> edge[100000]; // to store edges
bool included[100000]; // to keep track of elements in vertex cover set
bool done[100000]; // to keep track of undiscivered nodes to do DFS on tree
int cnt; // count the elements in vertex set
/* Function performs DFS and makes a vertex cover set */
bool solve(int source){
done[source] = true;
for(unsigned int i = 0; i<edge[source].size(); ++i){
if(!done[edge[source][i]]){ // if node is undiscovered
if(!solve(edge[source][i]) && !included[source]){ // if child node is not included and neither its parent
included[source] = true; // element added to vertex cover set
cnt++; // increasing the size of set
}
}
}
return included[source]; // return the status of current source vertex
}
int main(){
int n,u,v;
scanint(n);
for(int i = 0; i<n-1; ++i){
done[i] = false;
included[i] = false;
scanint(u);
scanint(v);
edge[u-1].push_back(v-1);
edge[v-1].push_back(u-1);
}
done[n-1] = false;
included[n-1] = false;
cnt = 0;
solve(0);
printf("%d\n", cnt);
return 0;
}
我的新源代码：
vector<int> edge[100000]; // to store edges
bool incld[100000]; // to keep track of nodes in vertex cover set
bool covrd[100000]; // to keep track of nodes already covered
bool done[100000]; // to keep track of undiscovered nodes to perform DFS
int cnt; // keep track of size of vertex cover set
/* Function to calculate vertex cover set via DFS */
void solve(int source){
int child; // to store index of child node
done[source] = true;
for(unsigned int i = 0; i<edge[source].size(); ++i){
if(!done[edge[source][i]]){ // if child node is undiscovered
child = edge[source][i];
if(incld[child]) // if child node is included in vertex set
covrd[source] = true; // setting current node to be covered
else if(!covrd[child] && !incld[source]){ // if child node is not covered and current node is not included in vertex set
incld[source] = true; // including current node
covrd[child] = true; // covering child node
cnt++; // incrementing size of vertex cover set
}
}
}
}
int main(){
int n,u,v;
scanint(n);
for(int i = 0; i<n-1; ++i){
done[i] = false;
incld[i] = false;
covrd[i] = false;
scanint(u);
scanint(v);
edge[u-1].push_back(v-1);
edge[v-1].push_back(u-1);
}
done[n-1] = false;
incld[n-1] = false;
covrd[n-1] = false;
cnt = 0;
solve(0);
printf("%d\n", cnt);
return 0;
}
请帮忙。