Leetcode::Construct Binary Tree from Inorder and Postorder Traversal

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *build( vector<int>&inorder, vector<int> &postorder,int in_s,int in_e, int pos_s, int pos_e)
    {
        if( in_s >= in_e )
        {
            return NULL;
        }
        
        int val = postorder[pos_e-1];
        
        TreeNode * tmp=new TreeNode(val);
        
        int i;
        
        for(i=in_s; i< in_e ; i++ )
        {
            if( val == inorder[i])
            {
                break;
            }
        }
        
        int len = i - in_s;
        
        tmp->left=build(inorder,postorder,in_s,i,pos_s ,pos_s + len);
        tmp->right=build(inorder,postorder,i+1,in_e,pos_s+len,pos_e -1);
        return tmp;
    }
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return build(inorder,postorder,0,inorder.size(),0,postorder.size());
    }
};