1138 Postorder Traversal (25 分)难度: 一般 / 知识点: 建树

Posted 2021-12-22 辉小歌

https://pintia.cn/problem-sets/994805342720868352/problems/994805345078067200
就是建树，然后遍历。

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int a[N],b[N],n;
unordered_map<int,int>mp,l,r;
int build(int l1,int r1,int l2,int r2)

    int root=a[l1];
    int k=mp[root];
    if(k>l2) l[root]=build(l1+1,l1+k-l2,l2,k-1);
    if(k<r2) r[root]=build(l1+k-l2+1,r1,k+1,r2);
    return root;

vector<int>ans;
void dfs(int u)

    if(l[u]) dfs(l[u]);
    if(r[u]) dfs(r[u]);
    ans.push_back(u);

int main(void)

    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=n;i++) cin>>b[i],mp[b[i]]=i;
    build(1,n,1,n);
    dfs(a[1]);
    cout<<ans[0];
    return 0;