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剑指offe

admin 11月 13, 2020 0

Problem

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

Solution

常规思路

class 
{
public:
    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin)
    {
        if (vin.size() <= 0 || pre.size() <= 0)
        {
            return NULL;
        }

        TreeNode* root = new TreeNode(pre[0]);

        vector<int> leftPre, leftVin, rightPre, rightVin;

        bool isRootLeft = true;

        for (int i = 0; i < vin.size(); ++i)
        {
            if(vin[i] == pre[0])
            {
                isRootLeft = false;
                continue;
            }

            if(isRootLeft)
            {
                leftVin.push_back(vin[i]);
                leftPre.push_back(pre[i+1]);
            }
            else
            {
                rightVin.push_back(vin[i]);
                rightPre.push_back(pre[i]);
            }
        }

        root->left = reConstructBinaryTree(leftPre, leftVin);
        root->right = reConstructBinaryTree(rightPre, rightVin);

        return root;
    }
};