TreeNode* createTree(int *arr, int length) {

    if(length<) return NULL;

    TreeNode* root = new TreeNode(arr[]);

    deque<pair<TreeNode*,int> > route;

    route.push_back(make_pair(root,));

    while(!route.empty()) {

        TreeNode* temp = route.front().first;

        int ct = route.front().second;

        route.pop_front();

        if(*ct+<length) {

            temp->left = new TreeNode(arr[*ct+]);//创建当前节点的左叶子

            route.push_back(make_pair(temp->left,*ct+));

        }

        if(*ct+<length) {

            temp->right = new TreeNode(arr[*ct+]);//创建当前节点的右叶子

            route.push_back(make_pair(temp->right,*ct+));

        }

    }

    return root;

}

void PostOrder(TreeNode* root) {

    deque<pair<TreeNode*, bool> > route;

    route.push_back(make_pair(root, false));

    while(!route.empty()) {

        TreeNode* root = route.back().first;

        bool visit = route.back().second;

        route.pop_back();

        if(root==NULL)

            continue;

        if(visit) {

            cout << root->val << ' ';

        } else {//改变下面三者的顺序就可以实现三种排序

            route.push_back(make_pair(root, true));

            route.push_back(make_pair(root->right, false));

            route.push_back(make_pair(root->left, false));

        }

    }

}