Problem 298: Binary Tree Longest Consecutive Sequence
https://leetcode.com/problems/binary-tree-longest-consecutive-sequence/

思路
涉及到二叉树的题目一般情况都要进行遍历(或者分治)。
可以用一个全局变量来维护 max 值,然后用一个 cur 变量来 track 进行到了哪一步。最后取最大值。
复杂度
Time:
Space:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
int max = 0;
public int longestConsecutive(TreeNode root) {
if (root == null) {
return 0;
}
helper(root, 0, root.val);
return max;
}
private void helper(TreeNode root, int cur, int target) {
if (root == null) {
return;
}
if (root.val == target) {
cur++;
} else {
cur = 1;
}
max = Math.max(max, cur);
helper(root.left, cur, root.val + 1);
helper(root.right, cur, root.val + 1);
}
}
易错点
递归函数的 parameters 都是变量,不能放常量,比如 target
helper(root.left, cur, root.val + 1);
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