lintcode73. 前序遍历和中序遍历树构造二叉树

根据前序遍历和中序遍历树构造二叉树.

样例
样例 1:

输入：[],[]
输出：{}
解释：
二叉树为空
样例 2:

输入：[2,1,3],[1,2,3]
输出：{2,1,3}
解释：
二叉树如下
  2
 / \
1   3
注意事项
你可以假设树中不存在相同数值的节点

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     *@param preorder : A list of integers that preorder traversal of a tree
     *@param inorder : A list of integers that inorder traversal of a tree
     *@return : Root of a tree
     */
    TreeNode * buildTree(vector<int> &preorder, vector<int> &inorder) {
        // write your code here
        map<int,int> index;
        for (int i = 0; i < inorder.size(); i++) {
            /* code */
            index[inorder[i]]=i;
        }
        return building(preorder,inorder,0,preorder.size()-1,0,inorder.size()-1,index);
    }
    TreeNode* building(vector<int> &preorder, vector<int> &inorder,int prestart, int preend ,int instart,int inend,map<int,int>index)
    {
        if(prestart>preend||instart>inend) return NULL;
        int i=index[preorder[prestart]];
        int len=i-instart;
        TreeNode*newroot=new TreeNode(preorder[prestart]);
        newroot->left=building(preorder,inorder,prestart+1,prestart+len,instart,i-1,index);
        newroot->right=building(preorder,inorder,prestart+len+1,preend,i+1,inend,index);
        return newroot;
    }
};

来源：CSDN

作者：Sinb妃

链接：https://blog.csdn.net/weixin_43981315/article/details/104159374