劍指offer——重建二叉樹

/**
 * 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* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
        int inlen = vin.size();
        if(inlen==0)
            return NULL;
        //創建根節點，肯定是前序遍歷的第一個節點
        TreeNode* root=new TreeNode(pre[0]);
        vector<int> left_pre,left_vin,right_pre,right_vin;
        //在中序遍歷中找到根節點
        int gen = 0;
        for(int i=0;i<inlen;i++) {
            if(vin[i]==pre[0]) {
                gen = i;
                break;
            }
        }
        //構建左右子樹的前序遍歷和中序遍歷
        for(int i=0;i<gen;i++) {
            left_pre.push_back(pre[i+1]);
            left_vin.push_back(vin[i]);
        }
        for(int i=gen+1;i<inlen;i++) {
            right_pre.push_back(pre[i]);
            right_vin.push_back(vin[i]);
        }
        root->left = reConstructBinaryTree(left_pre,left_vin);
        root->right = reConstructBinaryTree(right_pre,right_vin);

        return root;   
    }
};