蒟蒻刚学IO，不会a+b，求助

WA39 QwQ

如何正确的统计路径和？？

#include<bits/stdc++.h>
#define inf 0x7fffffff
#define ll long long
using namespace std;
int n,m;
#define maxn 200009 
int dfn[maxn],pos[maxn],size[maxn],top[maxn],deep[maxn],fa[maxn],son[maxn],cnt=0;
vector<int> v[maxn];
struct node{
    int l,r;
    int val,mark;
}tr[maxn*4];
void dfs(int x)
{
    size[x]=1;
    for(int i=0;i<v[x].size();i++)
    {
        int to=v[x][i];
        if(!size[to])
        {
            fa[to]=x;
            deep[to]=deep[x]+1;
            dfs(to);
            size[x]+=size[to];
            if(size[to]>size[son[x]])son[x]=to;
        }
    }
}
void dfs(int x,int tp)
{
    top[x]=tp;
    pos[x]=++cnt;
    dfn[cnt]=x;
    if(son[x])dfs(son[x],tp);
    for(int i=0;i<v[x].size();i++)
    {
        int to=v[x][i];
        if(!top[to])dfs(to,to);
    }
}
void Build(int x,int l,int r)
{
    tr[x].l=l,tr[x].r=r;
    if(l==r)
    {
        tr[x].mark=0;
        tr[x].val=0; 
        return;
    }
    int mid=(l+r)>>1;
    Build(x*2,l,mid);
    Build(x*2+1,mid+1,r);
    tr[x].mark=tr[x].val=0; 
}
void relese(int x)
{
    if(tr[x].l==tr[x].r||tr[x].mark==0)return;
    tr[x*2].val+=(tr[x*2].r-tr[x*2].l+1)*tr[x].mark;
    tr[x*2].mark=tr[x].mark;
    tr[x*2+1].val+=(tr[x*2+1].r-tr[x*2+1].l+1)*tr[x].mark;
    tr[x*2+1].mark=tr[x].mark;
    tr[x].mark=0; 
}
void Add(int x,int l,int r,int val)
{
    if(l<=tr[x].l&&tr[x].r<=r)
    {
        tr[x].mark+=val;
        tr[x].val+=(tr[x].r-tr[x].l+1)*val;
        return;
    }
    relese(x);
    int mid=(tr[x].l+tr[x].r)>>1;
    if(l<=mid)Add(x*2,l,r,val);
    if(r>mid)Add(x*2+1,l,r,val);
    tr[x].val=tr[x*2].val+tr[x*2+1].val;
}
int Sum(int x,int l,int r)
{
    if(l<=tr[x].l&&tr[x].r<=r)
    {
        return tr[x].val;
    }
    relese(x);
    int mid=(tr[x].l+tr[x].r)>>1;
    int ans=0;
    if(l<=mid)ans+=Sum(x*2,l,r);
    if(r>mid)ans+=Sum(x*2+1,l,r);
    return ans; 
}
int LCA(int x,int y,bool f=0)
{
    int res=0;
    while(top[x]!=top[y])
    {
        if(deep[top[x]]<deep[top[y]])swap(x,y);
        if(!f)res+=Sum(1,pos[top[x]],pos[x]);
        if(f)Add(1,pos[top[x]],pos[x],1);
        x=fa[top[x]];
    }
    if(x==y)return res;
    if(pos[x]>pos[y])swap(x,y);
    if(!f)res+=Sum(1,pos[x]+1,pos[y]);
    if(f) Add(1,pos[x]+1,pos[y],1);
    return res; 
}
signed main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n-1;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    dfs(1),dfs(1,1);
    Build(1,1,n);
    while(m--)
    {
        char cz[9];
        scanf("%s",cz);
        int x,y;
        scanf("%d%d",&x,&y);
        if(cz[0]=='P')
        {
            LCA(x,y,1);
        }else
        {
            printf("%d\n",LCA(x,y));
        }
    }
    return 0;
}