leetcode Construct Binary Tree from Preorder and Inorder Traversal

方法类似Construct Binary Tree from Postorder and Inorder Traversal          http://blog.csdn.net/menyangyang/article/details/38686975

代码

class Solution{public:TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder){TreeNode *head = NULL;int inSize = inorder.size();int preSize = preorder.size();if(inSize!=preSize||inSize==0)return head;return buildTreeHelper(inorder, 0, inSize-1, preorder, 0, preSize-1);            }TreeNode * buildTreeHelper(vector<int> &inorder,int start0, int end0 ,vector<int> &preorder,int start1, int end1){if(start0>end0||start1>end1)return NULL;TreeNode *node = new TreeNode(preorder[start1]);int leftNum = 0;int mid;for(int i = start0; i <= end0; ++i){if(inorder[i]==node->val){    mid = i;break;}}        leftNum = mid - start0;node->left = buildTreeHelper(inorder,start0, mid-1 ,preorder, start1+1, start1+leftNum);node->right = buildTreeHelper(inorder,mid+1, end0, preorder, start1+leftNum+1, end1);return node;}};