검지 offer 문제 4 재건 두 갈래 나무

 
 ， 。
 。
 {1,2,4,7,3,5,6,8} {4,7,2,1,5,3,8,6}， 。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    struct TreeNode* construct(vector pre, int ps, int pe, vector vin, int vs, int ve)
    {
        TreeNode* node = new TreeNode(pre[ps]);
        int i;
        for(i = vs; vin[i] != node->val; i++);
        int l = i - vs;
        int r = ve - i;
        if(l)
            node->left = construct(pre, ps+1, ps+l, vin, vs, vs+l-1);
        else
            node->left = nullptr;
        if(r)
            node->right = construct(pre, pe-r+1, pe, vin, ve-r+1, ve);
        else
            node->right = nullptr;
        return node;
    }
    struct TreeNode* reConstructBinaryTree(vector pre,vector vin) 
    {
        if(pre.size() == 0 || vin.size() == 0 || pre.size() != vin.size())
            return nullptr;
        return construct(pre, 0, pre.size()-1, vin, 0, vin.size()-1);
    }
};