为什么栈这样写才对？

正确的：

#include<bits/stdc++.h>
#define int long long
#define maxn 40005
#define Q 1e7
using namespace std;
inline int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){
        if(ch=='-')f=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')x=x*10+ch-'0',ch=getchar();
    return x*f;
}
inline void write(int x){
    if(x<0){putchar('-');x=-x;}
    if(x>=10)write(x/10);
    putchar(x-x/10*10+'0');return;
}
int n,m,siz[maxn],f[maxn],tot,ask[105],ROOT;
bool vis[maxn],ans[10000005],have[10000005];
struct EDGE{int v,w;};
vector<EDGE>edge[maxn];
inline int size(int rt,int fa){
    ++tot;siz[rt]=1;
    for(auto i:edge[rt]){
        int v=i.v;if(vis[v]||v==fa)continue;
        siz[rt]+=size(v,rt);
    }
    return siz[rt];
}
inline void dp(int rt,int fa){
    f[rt]=tot-siz[rt];
    for(auto i:edge[rt]){
        int v=i.v;
        if(v==fa||vis[v])continue;
        f[rt]=max(f[rt],siz[v]);
        dp(v,rt);
    }
    if(f[rt]<f[ROOT])ROOT=rt;
}
int tong[10000005],top;
inline void get(int rt,int fa,int dis){
    tong[top++]=dis;
    for(auto i:edge[rt]){
        int v=i.v,w=i.w;
        if(vis[v]||v==fa)continue;
        get(v,rt,dis+w);
    }
}
inline void calc(int rt){
    tot=0;size(rt,rt);
    ROOT=rt;dp(rt,rt);
    have[0]=true;top=1;tong[0]=0;int res;
    for(auto i:edge[ROOT]){
        int v=i.v,w=i.w;
        if(vis[v])continue;
        res=top;get(v,ROOT,w);
        for(int j=1;j<=m;++j)for(int k=res;k<top&&(!ans[j]);++k)
        if(tong[k]<=ask[j])ans[j]=have[ask[j]-tong[k]];
        --res;
        while(++res<top)if(tong[res]<=Q)have[tong[res]]=true;
    }
    while(top--)if(tong[top]<=Q)have[tong[top]]=false;
    vis[ROOT]=true;
    for(auto i:edge[ROOT]){
        if(vis[i.v])continue;
        calc(i.v);
    }
}
signed main(){
    n=read();m=read();
    for(int i=1;i<n;++i){
        int u=read(),v=read(),w=read();
        edge[u].push_back({v,w});
        edge[v].push_back({u,w});
    }
    for(int i=1;i<=m;++i)ask[i]=read();
    calc(1);
    for(int i=1;i<=m;++i){
        if(ans[i])cout<<"AYE\n";
        else cout<<"NAY\n";
    }
    return 0;
}

错误的：

#include<bits/stdc++.h>
#define int long long
#define maxn 10005
#define Q 1e7
using namespace std;
inline int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){
        if(ch=='-')f=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')x=x*10+ch-'0',ch=getchar();
    return x*f;
}
inline void write(int x){
    if(x<0){putchar('-');x=-x;}
    if(x>=10)write(x/10);
    putchar(x-x/10*10+'0');return;
}
int n,m,siz[maxn],f[maxn],tot,ask[105],ROOT;
bool vis[maxn],ans[10000005],have[10000005];
struct EDGE{int v,w;};
vector<EDGE>edge[maxn];
inline int size(int rt,int fa){
    ++tot;siz[rt]=1;
    for(auto i:edge[rt]){
        int v=i.v;if(vis[v]||v==fa)continue;
        siz[rt]+=size(v,rt);
    }
    return siz[rt];
}
inline void dp(int rt,int fa){
    f[rt]=tot-siz[rt];
    for(auto i:edge[rt]){
        int v=i.v;
        if(v==fa||vis[v])continue;
        f[rt]=max(f[rt],siz[v]);
        dp(v,rt);
    }
    if(f[rt]<f[ROOT])ROOT=rt;
}
int tong[10000005],top;
inline void get(int rt,int fa,int dis){
    tong[++top]=dis;
    for(auto i:edge[rt]){
        int v=i.v,w=i.w;
        if(vis[v]||v==fa)continue;
        get(v,rt,dis+w);
    }
}
inline void calc(int rt){
    tot=0;size(rt,rt);
    ROOT=rt;dp(rt,rt);
    have[0]=true;top=1;tong[1]=0;int res;
    for(auto i:edge[ROOT]){
        int v=i.v,w=i.w;
        if(vis[v])continue;
        res=top;get(v,ROOT,w);
        for(int j=1;j<=m;++j)for(int k=res+1;k<=top&&(!ans[j]);++k)
        if(tong[k]<=ask[j])ans[j]=have[ask[j]-tong[k]];res--;
        while(++res<top)if(tong[res]<=Q)have[tong[res]]=true;
    }
    while(top--)if(tong[top]<=Q)have[tong[top]]=false;
    vis[ROOT]=true;
    for(auto i:edge[ROOT]){
        if(vis[i.v])continue;
        calc(i.v);
    }
}
signed main(){
    n=read();m=read();
    for(int i=1;i<n;++i){
        int u=read(),v=read(),w=read();
        edge[u].push_back({v,w});
        edge[v].push_back({u,w});
    }
    for(int i=1;i<=m;++i)ask[i]=read();
    calc(1);
    for(int i=1;i<=m;++i){
        if(ans[i])cout<<"AYE\n";
        else cout<<"NAY\n";
    }
    return 0;
}