UVA 548(p155)----Tree

#include<bits/stdc++.h>
using namespace std;
const int INF=1e7;
const int maxn=1e5;
int n,ans,ansu;
int lch[maxn],rch[maxn];
int mid[maxn],last[maxn];
int input(int*a)
{
    string st;
    if(!getline(cin,st)) return 0;
    stringstream ss(st);
    int tmp;
    n=0;
    while(ss>>tmp) a[n++]=tmp;
    return n>0;
}
int build(int l1,int r1,int l2,int r2)
{
    if(l1>r1) return 0;
    int root=last[r2];
    int p=l1;
    while(mid[p]!=root) p++;
    int num=p-l1;
    lch[root]=build(l1,p-1,l2,l2+num-1);
    rch[root]=build(p+1,r1,l2+num,r2-1);
    return root;
}
void solve(int u,int sum)
{
    sum+=u;
    if(!lch[u]&&!rch[u])
    {
        if(sum<ans||(sum==ans&&ansu>u))
        {
            ansu=u;
            ans=sum;
        }
    }
    if(lch[u]) solve(lch[u],sum);
    if(rch[u]) solve(rch[u],sum);
}
int main()
{
    ios::sync_with_stdio(0);
    while(input(mid))
    {
        input(last);
        build(0,n-1,0,n-1);
        ansu=0;
        ans=INF;
        solve(last[n-1],0);
        cout<<ansu<<endl;
    }
    return 0;
}

题目地址：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=489