Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target…

  Given a string that consists of only uppercase English letters, you can replace any letter in the strin…

1. 题目 Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For examp…

Medium Given a nested list of integers, return the sum of all integers in the list weighted by their depth. Ea…

题意：爬楼梯，一次可以爬1阶或2阶，输入正数n，输出爬到n阶楼梯总共有几种策略。 解题思路： 方法一：动态规划DP，一次可以上1阶或2阶，那么到第n阶可以从第n-1阶上1阶，或者从n-2阶上2阶，所以到第n阶的策略等于到…

27. 移除元素 问题 给定一个数组 和一个值 ，你需要原地移除所有数值等于 的元素，返回移除后数组的新长度。 不要使用额外的数组空间，你必须在原地修改输入数组并在使用 额外空间的条件下完成。 元素的顺序可以改变。你不需…

  Chapter 1. Arrays and Strings 1.1 Unique Characters of a String 1.2 Reverse String 1.3 Permutation Stri…

  Given a text file file.txt that contains list of phone numbers (one per line), write a one liner bash s…

  Given the root node of a binary search tree (BST) and a value to be inserted into the tree, insert…

Rotate List Given a list, rotate the list to the right by k places, where k is non-negative. For example: Give…

1. 题目 Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 39…

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999. 思路…