Given an unsorted integer array, find the smallest missing positive integer.

Given a 32-bit signed integer, reverse digits of an integer.

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

Given a string, find the length of the longest substring without repeating characters.

正式刷题第三天。之前看了个说法，挺认可的。就是不要太在意一天的能呈现的价值，但是要在意累计的价值。之前很多时候我会对今天一天没有完成的计划而沮丧，事实上，算法的实践，统计学的学习这些都是需要时间去…

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Given n non-negative integers a1, a2, …, an , where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find …

给定一个排序数组，你需要在原地删除重复出现的元素，使得每个元素只出现一次，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 O(1) 额外空间的条件下完成。

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)