Leetcode面試題9——根據前序和中序遍歷序列來建立二叉樹

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* constructTree(vector<int>&preorder,vector<int>&inorder,int pre_start,int pre_end,int in_start,int in_end)
    {
        if(pre_start>pre_end)return NULL;
        int cur_num=preorder[pre_start];
        TreeNode* root=new TreeNode(cur_num);
        int index;
        for(int i=in_start;i<=in_end;i++)
        {
            if(inorder[i]==cur_num)
            {
                index=i;
                break;
            }
        }
        root->left=constructTree(preorder,inorder,pre_start+1,pre_start+index-in_start,in_start,index-1);
        root->right=constructTree(preorder,inorder,pre_start+index-in_start+1,pre_end,index+1,in_end);
        return root;      
    }
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
            int len=preorder.size();
            return constructTree(preorder,inorder,0,len-1,0,len-1);
    }
};