（树）根据中序后序构建二叉树

class Solution {
public:
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        vector<int>::size_type lenIn = inorder.size();
        vector<int>::size_type lenPost = postorder.size();
        return buildTree_Aux(inorder,0,lenIn-1,postorder,0,lenPost-1);
    }

    TreeNode *buildTree_Aux(vector<int> &inorder,int inB,int inE,
                            vector<int> &postorder,int poB,int poE) {
        if(inB > inE || poB > poE)
            return NULL;
        //在后序遍历中确定根节点
        TreeNode* root = new TreeNode(postorder[poE]);
        //在中序遍历中确定左右子树
        vector<int>::iterator iter = find(inorder.begin()+inB,inorder.begin()+inE,postorder[poE]);
        int index = iter - inorder.begin();//根节点的位置
        root->left = buildTree_Aux(inorder,inB,index-1,postorder,poB,poB+index-1-inB);　　    //这里postorder,poB,poB+index-1-inB这部分表示后序的左子树。pob是开始位置，index-1-inB是后序左子树的节点数的个数。poB+index-1-inB是后序的左子树的尾部
        root->right = buildTree_Aux(inorder,index+1,inE,postorder,poB+index-inB,poE-1);　　    //这里postorder,poB+index-inB,poE-1这部分表示后序的右子树。poB+index-inB右子树开始位置，poE-1右子树结束位置，去掉了根节点的值（最尾部）
        return root;
    }
};

/**
 * 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 *buildTree(vector<int> &preorder, vector<int> &inorder) {
        vector<int>::size_type lenIn = inorder.size();
        vector<int>::size_type lenPre = preorder.size();
        return buildTree_Aux(preorder, 0, lenPre-1, inorder, 0, lenIn-1);
    }
     TreeNode *buildTree_Aux(vector<int> &preorder,int prb,int pre,
                             vector<int> &inorder,int inb,int ine) {
         if (prb > pre || inb > ine)
             return NULL;
         TreeNode *root = new TreeNode(preorder[prb]);
         vector<int>::iterator iter = find(inorder.begin()+inb,inorder.begin()+ine,preorder[pre]);
         int mid = iter - inorder.begin();
         root->left = buildTree_Aux(preorder, prb+1, prb+mid-inb, inorder, inb, mid-1);
         root->right = buildTree_Aux(preorder, prb+1+mid-inb, pre, inorder, mid+1, ine);
         return root;
     }
};