/
MaximumDifferenceBetweenNodeAndAncestors.java
71 lines (59 loc) · 1.7 KB
/
MaximumDifferenceBetweenNodeAndAncestors.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/maximum-difference-between-node-and-ancestor
class Solution {
public int maxAncestorDiff(TreeNode root) {
ValueTracker tracker = new ValueTracker();
dfs(root, tracker);
return tracker.maxDiff;
}
void dfs(TreeNode root, ValueTracker tracker) {
if (root == null) {
return;
}
tracker.track(root.val);
dfs(root.left, tracker);
dfs(root.right, tracker);
tracker.untrack(root.val);
}
class ValueTracker {
Stack<Integer> maxStack = new Stack<>();
Stack<Integer> minStack = new Stack<>();
int maxDiff = 0;
ValueTracker() {
}
void track(int x) {
if (maxStack.isEmpty() || x >= maxStack.peek()) {
maxStack.push(x);
}
if (minStack.isEmpty() || x <= minStack.peek()) {
minStack.push(x);
}
maxDiff = Math.max(maxDiff, maxStack.peek() - minStack.peek());
}
void untrack(int x) {
if (x == maxStack.peek()) {
maxStack.pop();
}
if (x == minStack.peek()) {
minStack.pop();
}
}
public String toString() {
return "max = " + maxStack + ", min = " + minStack;
}
}
}