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  • 【leetcode】1038. Binary Search Tree to Greater Sum Tree

    题目如下:

    Given the root of a binary search tree with distinct values, modify it so that every node has a new value equal to the sum of the values of the original tree that are greater than or equal to node.val.

    As a reminder, a binary search tree is a tree that satisfies these constraints:

    • The left subtree of a node contains only nodes with keys less than the node's key.
    • The right subtree of a node contains only nodes with keys greater than the node's key.
    • Both the left and right subtrees must also be binary search trees.

    Example 1:

    Input: [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
    Output: [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
    

    Note:

    1. The number of nodes in the tree is between 1 and 100.
    2. Each node will have value between 0 and 100.
    3. The given tree is a binary search tree.

    解题思路:我的方法简单粗暴,第一次遍历树,把树中每个节点的值存入list;接下来再遍历一次,对于每个node,在list中找出所有值比自己大的元素的和,加上node自身的值,即为这个node的新值。

    代码如下:

    # Definition for a binary tree node.
    # class TreeNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.left = None
    #         self.right = None
    
    class Solution(object):
        val_list = []
        def recursive(self,node):
            self.val_list.append(node.val)
            if node.right != None:
                self.recursive(node.right)
            if node.left != None:
                self.recursive(node.left)
    
        def reValue(self,node):
            inx = self.val_list.index(node.val)
            node.val += sum(self.val_list[inx+1:])
            if node.right != None:
                self.reValue(node.right)
            if node.left != None:
                self.reValue(node.left)
    
        def bstToGst(self, root):
            """
            :type root: TreeNode
            :rtype: TreeNode
            """
            if root != None:
                self.val_list = []
                self.recursive(root)
                self.val_list.sort()
                self.reValue(root)
            return root
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  • 原文地址:https://www.cnblogs.com/seyjs/p/11026162.html
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