求助，为什么单向边过不了，双向边可以AC

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<cmath>
using namespace std;
int fread(){
	int s=0,x=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-') x=-1;
		ch=getchar();
	}
	while(ch<='9'&&ch>='0'){
		s=s*10+(ch-'0');
		ch=getchar();
	}
	return x?s:-s;
}

struct node{
	int val;
	bool G;
	bool H;
}fa[100005][30];
char ned;
string c;
vector<int> edge[100005];
int deep[100005];
int gh[100005];
int n,m,u,v,a,b,temp;

void dfs( int now , int father){
	
	deep[now]=deep[father]+1;
	
	fa[now][0].val=father;
	fa[now][0].G=(gh[now]==1||gh[father]==1);
	fa[now][0].H=(gh[now]==2||gh[father]==2);
	for(int i=1;(1<<i)<=deep[now];i++){
	    
		  fa[now][i].val=fa[fa[now][i-1].val][i-1].val;
          fa[now][i].G=(fa[fa[now][i-1].val][i-1].G||fa[now][i-1].G);
          fa[now][i].H=(fa[fa[now][i-1].val][i-1].H||fa[now][i-1].H);
          
	}

	for(int i=0;i<edge[now].size();i++){
	
		int next=edge[now][i];
        if(next!=father)
		dfs(next,now);
	}
}

bool lca(int a ,int b, int c){
	if(deep[a]<deep[b]) swap(a,b);
	int h=deep[a]-deep[b];
	int k=log2(h);
	for(int i=k;i>=0;i--){
		if(h&(1<<i)){
		if(c==1&&fa[a][i].G) {
			return 1;
		}
		if(c==2&&fa[a][i].H){
			return 1;
		} 
        a=fa[a][i].val;
    }
	}

	if(a==b) {
		if(gh[a]==c)return 1;
		return 0; 
	}

	k=log2(deep[a]);
	for(int i=k;i>=0;i--){
		if(fa[a][i].val!=fa[b][i].val){
		if(c==1){
			if(fa[a][i].G||fa[b][i].G)return 1;
		}
		else if(c==2){
			if(fa[a][i].H||fa[b][i].H)return 1;
		}
			a=fa[a][i].val;
			b=fa[b][i].val;
		}
	}
	if(c==1){
		if(fa[a][0].G||fa[b][0].G)return 1;
	}
	if(c==2){
		if(fa[a][0].H||fa[b][0].H)return 1;
	}
	return 0;
}

int main(){

	n=fread();m=fread();
    cin>>c;
    for(int i=n-1;i>=0;i--){
    	c[i+1]=c[i];
	}
	for(int i=1;i<=n;i++){
		if(c[i]=='G')gh[i]=1;
		else gh[i]=2;
	}
	for(int i=1;i<n;i++){

		u=fread();
		v=fread();
		edge[u].push_back(v);
        edge[v].push_back(u);//原来没有这一句 
	}
	
	dfs(1,0);
	
	for(int i=1;i<=m;i++){
		a=fread();b=fread();cin>>ned;
		if(ned=='H') temp=2;
		else temp=1;
		printf("%d",lca(a,b,temp));
	}
	return 0;
}