[面试真题] LeetCode：Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:You may assume that duplicates do not exist in the tree.

解法：递归求解，思路同上一篇博客中用先序和中序构造二叉树类似。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    TreeNode *buildTree(vector<int> &postorder,int ph, int pe, vector<int> &inorder, int ih, int ie){
         TreeNode *root;
         if(pe - ph < 0){
             return NULL;
         }
         root = new TreeNode(postorder[pe]);
         int index = ih-1;
         while(++index <= ie && inorder[index] != postorder[pe]){
         }
         int leftPostLen = index - ih;
         root->left = buildTree(postorder, ph, ph+leftPostLen-1, inorder, ih, index-1);
         root->right = buildTree(postorder, ph+leftPostLen, pe-1, inorder, index+1, ie);
         return root;
     }
    
public:
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return buildTree(postorder, 0, postorder.size()-1, inorder, 0, inorder.size()-1);
    }
};

Run Status: Accepted!
Program Runtime: 152 milli secs

Progress: 202/202 test cases passed.