1020 Tree Traversals (25 分) 后序和中序构建树

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思路

1. 后序和中序构造二叉树
2. 唯一一个注意的地方，在注释中。
3. CSDN真垃圾，c++没高亮，还要写成c

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<queue>
#include<vector>
using namespace std;const int MAXN=10005;
int n=0;
int postorder[MAXN],inorder[MAXN];struct Node{int val=-1;Node*left=NULL,*right=NULL;Node(int val_=0):val(val_){}
};int findPos(int val,int left,int right){for(int i=left;i<=right;i++){if(val==inorder[i]){return i;}}return -1;
}Node* makeTree(int pos,int pos_inl,int pos_inr){if(pos_inl>pos_inr){return NULL;}Node *node=NULL;node=new Node(postorder[pos]);int pos_in_inorder=findPos(postorder[pos],pos_inl,pos_inr);int right_num=pos_inr-pos_in_inorder;// 注意这里是pos-right_num-1而不是想当然的pos_inr-1，这两个的位置并不一定对应node->left=makeTree(pos-right_num-1,pos_inl,pos_in_inorder-1);node->right=makeTree(pos-1,pos_in_inorder+1,pos_inr);return node;
}vector<int>res;
void levelSearch(Node*root){if(root==NULL){return;}queue<Node*>q;q.push(root);while(!q.empty()){Node* top=q.front();q.pop();res.push_back(top->val);if(top->left){q.push(top->left);}if(top->right){q.push(top->right);}}
}
int main(){cin>>n;for(int i=0;i<n;i++){scanf("%d",&postorder[i]);}for(int i=0;i<n;i++){scanf("%d",&inorder[i]);}Node* root=NULL;root=makeTree(n-1,0,n-1);levelSearch(root);
//    cout<<"size: "<<res.size()<<endl;for(int i=0;i<res.size();i++){if(!i){printf("%d",res[i]);}else{printf(" %d",res[i]);}}printf("\n");return 0;
}

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