剑指Offer总结——重建二叉树

/**
 * 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 len = pre.size();
        if(len==0) {
            return nullptr;
        }
        int root = pre[0];
        vector<int> leftPre, leftIn, rightPre, rightIn;
        TreeNode *ret = new TreeNode(root);
        int inRootIdx = 0;
        
        for(inRootIdx=0; inRootIdx < len; ++inRootIdx) {
            if(vin[inRootIdx] == root) {
                break;
            }
        }
        
        for(int i=0; i < len; ++i) {
            if(i < inRootIdx) {
                leftPre.push_back(pre[i+1]);
                leftIn.push_back(vin[i]);
            }
            else if(i>inRootIdx) {
                rightPre.push_back(pre[i]);
                rightIn.push_back(vin[i]);
            }
        }
        ret->left = reConstructBinaryTree(leftPre, leftIn);
        ret->right = reConstructBinaryTree(rightPre, rightIn);
        return ret;
    }
};