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BinarySearchTreeToGreaterSumTree.java
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BinarySearchTreeToGreaterSumTree.java
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
// https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree
class Solution {
public TreeNode bstToGst(TreeNode root) {
List<Integer> collect = new ArrayList<>();
Map<Integer, Integer> map = new HashMap<>();
dfs(root, collect, null);
int cum = 0, last = -1;
for (int i = collect.size() - 1; i >= 0; i--) {
int x = collect.get(i);
if (x != last) {
map.put(x, cum);
}
cum += x;
last = x;
}
dfs(root, collect, map);
return root;
}
void dfs(TreeNode root, List<Integer> collect, Map<Integer, Integer> map) {
if (root == null) {
return;
}
if (map == null) {
dfs(root.left, collect, map);
collect.add(root.val);
dfs(root.right, collect, map);
} else {
root.val += map.get(root.val);
dfs(root.left, collect, map);
dfs(root.right, collect, map);
}
}
}