09 2021 档案

Tree 系列（四） LCA
摘要：236. Lowest Common Ancestor of a Binary Tree Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. According to t 阅读全文

posted @ 2021-09-30 11:14 xiaoyongyong 阅读(167) 评论(0) 推荐(0)

Binary Search Tree 系列题目 98, 99, 96, 95, 450, 1008, 1373, 333,
摘要：/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { 阅读全文

posted @ 2021-09-27 00:03 xiaoyongyong 阅读(102) 评论(0) 推荐(0)

聊天系统设计 how to design a chat system
摘要：Senario: 1) one to one send message 2) sent/deleveried/read 3) user online status , online/last seen 5min 4) send image, video,file 5) group chat DAU: 阅读全文

posted @ 2021-09-26 02:45 xiaoyongyong 阅读(462) 评论(0) 推荐(0)

majority 求众数系列题目 169,229,48
摘要：169. Majority ElementGiven an array nums of size n, return the majority element.The majority element is the element that appears more than ⌊n / 2⌋ tim 阅读全文

posted @ 2021-09-25 23:16 xiaoyongyong 阅读(64) 评论(0) 推荐(0)

Tree traversal / serialize and deserialize 889, 222, 297,
摘要：public class TreeNode { int val; TreeNode left; TreeNode right; TreeNode() {} TreeNode(int val) { this.val = val; } TreeNode(int val, TreeNode left, T 阅读全文

posted @ 2021-09-16 21:44 xiaoyongyong 阅读(72) 评论(0) 推荐(0)

segment tree
摘要：数组实现方式（类似与heap的实现方式）： class NumArray { int[] arr=null; int len = 0; public NumArray(int[] nums) { len = nums.length; arr = new int[len*10]; buildSegTr 阅读全文

posted @ 2021-09-12 23:31 xiaoyongyong 阅读(97) 评论(0) 推荐(0)