Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexicographical order among all possible results. Example: Given "bcabc&q…

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between i and j is at most k. 这道题跟之前两道Contains Duplicate 包含重复值和Conta…

Given an array of integers and an integer k, return true if and only if there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i and j is at most k. (Old Version) Given an array of integers and an i…

Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct. 这道题不算难题,就是使用一个哈希表,遍历整个数组,如果哈希表里存在,返回fal…

Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id. +----+------------------+ | Id | Email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com |…

原题链接在这里:https://leetcode.com/problems/remove-duplicate-letters/ 题目: Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexic…

Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of any oneof them. Two trees are duplicate if they have the same structure with same node values. Example 1: 1 / \ 2 3 / /…

Given a list of directory info including directory path, and all the files with contents in this directory, you need to find out all the groups of duplicate files in the file system in terms of their paths. A group of duplicate files consists of at l…

原题链接在这里:https://leetcode.com/problems/find-duplicate-file-in-system/description/ 题目: Given a list of directory info including directory path, and all the files with contents in this directory, you need to find out all the groups of duplicate files in…

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between i and j is at most k. SOL1: public class Solution { public b…