leetcode-1038

leetcode 1038

每个数加上大于或者等于它的数，根据二叉搜索树特点进行 右-中-左的遍历，其中操作处理节点值相加

/**
 * 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* bstToGst(TreeNode* root) {
        if(root)
            dfs(root);
        return root;
    }
private:
    int pre = 0;
    void dfs(TreeNode* node) {
        if(node) {
            dfs(node->right);
            node->val += pre;
            pre = node->val;
            dfs(node->left);
        }
    }
};