LeetCode: Binary Tree Longest Consecutive Sequence Posted on July 25, 2018July 26, 2020 by braindenny Binary Tree Longest Consecutive Sequence Similar Problems: LeetCode: Binary Tree Longest Consecutive Sequence II CheatSheet: Leetcode For Code Interview CheatSheet: Common Code Problems & Follow-ups Tag: #binarytree, #treetraversal, #classic Given a binary tree, find the length of the longest consecutive sequence path. The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from parent to child (cannot be the reverse). Example 1: Input: 1 \ 3 / \ 2 4 \ 5 Output: 3 Explanation: Longest consecutive sequence path is 3-4-5, so return 3. Example 2: Input: 2 \ 3 / 2 / 1 Output: 2 Explanation: Longest consecutive sequence path is 2-3, not 3-2-1, so return 2. Github: code.dennyzhang.com Credits To: leetcode.com Leave me comments, if you have better ways to solve. Solution: // https://code.dennyzhang.com/binary-tree-longest-consecutive-sequence // Basic Ideas: pre-order // // Complexity: Time O(n), Space O(1) /** * Definition for a binary tree node. * type TreeNode struct { * Val int * Left *TreeNode * Right *TreeNode * } */ func preOrder(root *TreeNode, maxCnt *int) int { if root == nil { return 0 } res := 1 var count int if root.Left != nil { count = 1 v := preOrder(root.Left, maxCnt) if root.Val + 1 == root.Left.Val { count = v + 1 } if count > res { res = count } } if root.Right != nil { count = 1 v := preOrder(root.Right, maxCnt) if root.Val + 1 == root.Right.Val { count = v + 1 } if count > res { res = count } } if res > *maxCnt { *maxCnt = res } return res } func longestConsecutive(root *TreeNode) int { maxCnt := 0 preOrder(root, &maxCnt) return maxCnt } Post Views: 4