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4_重建二叉树.cpp
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4_重建二叉树.cpp
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/**
* 输入某二叉树的前序遍历和中序遍历的结果,请重建出该二叉树。假设输入的前序遍历和中序遍历的结
* 果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6},则重建二叉树并返回。
*
* 常规题:前中序重建,递归重建即可,注意分割左右子树的时候的边界范围就可以了。
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* build(vector<int>&pre,vector<int>&vin,int pi,int pj,int vi,int vj)
{
if(pi>pj||vi>vj)
return NULL;
TreeNode* r=new TreeNode(pre[pi]);
int v=pre[pi],dex=0;
for(;dex+vi<=vj;++dex)
if(vin[dex+vi]==v)
break;
r->left=build(pre,vin,pi+1,pi+dex,vi,vi+dex-1);
r->right=build(pre,vin,pi+dex+1,pj,vi+dex+1,vj);
return r;
}
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
TreeNode *Root=build(pre,vin,0,pre.size()-1,0,vin.size()-1);
return Root;
}
};