参考文献
https://www.acwing.com/solution/content/64899/
C++ 代码
#include<bits/stdc++.h>
using namespace std;
struct node
{
int data;
node* left, *right;
node(int _da=0):data(_da){
left = nullptr;
right = nullptr;
}
};
const int N = 5e4+10;
int pre[N], ino[N];
vector<int> res;
unordered_map<int, int> mp;
int n = 0;
node* create(int il, int ir, int pl, int pr)
{
// if(il > ir) return nullptr;
node* root = new node(pre[pl]);
int k = mp[pre[pl]];
if(k > il) //此处如果加了if判断,则必须在node的构造函数中显示初始化letf指针和right指针,否则会导致段错误
root->left = create(il,k-1,pl+1,pl+k-il);
if(k < ir ) root->right = create(k+1, ir,pl+k-il+1,pr);
return root;
}
void postorder(node* root)
{
if(root == nullptr) return;
postorder(root->left);
postorder(root->right);
res.push_back(root->data);
}
int main()
{
scanf("%d", &n);
for(int i = 0; i < n; ++i) scanf("%d", &pre[i]);
for(int i = 0; i < n; ++i)
{
scanf("%d", &ino[i]);
mp[ino[i]] = i;
}
auto root = create(0,n-1,0,n-1);
postorder(root);
printf("%d\n", res[0]);
return 0;
}