C++详解Leetcode:105. Construct Binary Tree from Preorder and Inorder Traversal

原题

思路

code

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
int l1 = 0;
int l2 = 0;
int r1 = preorder.size() - 1;
int r2 = inorder.size() - 1;
TreeNode *s = (TreeNode*)malloc(sizeof(TreeNode));
//s = NULL;
s = CreateBT(preorder, inorder, l1, r1, l2, r2);
return s;
}

TreeNode* CreateBT(vector<int>& preorder, vector<int>& inorder, int l1, int r1, int l2, int r2)
{
TreeNode* s;
int i;
if (l1 > r1)
return NULL;
s = (TreeNode*)malloc(sizeof(TreeNode));
s->left = s->right = NULL;
for (i = l2; i <= r2; i++)
{
if (inorder[i] == preorder[l1])
{
break;
}
}
s->val = inorder[i];
s->left = CreateBT(preorder, inorder, l1 + 1, l1 + i - l2, l2, i - 1);
s->right = CreateBT(preorder, inorder, l1 + i - l2 + 1, r1, i + 1, r2);
return s;
}
};