Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
You may assume the integer do not contain any leading zero, except the number 0 itself.
The digits are stored such that the most significant digit is at the head of the list.
题目的意思即，用数组按从高位到低位的顺序表示一个非0的正整数。然后计算该整数 + 1后的结果。仍用数组表示。
Given a string s consists of upper/lower-case alphabets and empty space characters ‘ ‘, return the length of last word in the string.
If the last word does not exist, return 0.
Note: A word is defined as a character sequence consists of non-space characters only.
Example:
Input: “Hello World” Output: 5
简单题，计算字符串最后一个非空字符串的长度。
Find the contiguous subarray within an array (containing at least one number) which has the largest sum.
For example, given the array [-2,1,-3,4,-1,2,1,-5,4], the contiguous subarray [4,-1,2,1] has the largest sum = 6.
click to show more practice.
More practice: If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.
题目的意思是求一个数组，最大子序列的和。 并且，额外要求，在O(n)算法之外，可以尝试用分治法解决该问题。
The count-and-say sequence is the sequence of integers with the first five terms as following:
1 is read off as “one 1” or 11. 11 is read off as “two 1s” or 21. 21 is read off as “one 2, then one 1” or 1211. Given an integer n, generate the nth term of the count-and-say sequence.
Note: Each term of the sequence of integers will be represented as a string.
Example 1:
Input: 1 Output: “1” Example 2:
Input: 4 Output: “1211”
题目的意思就是反复的计算字符中，从左向右，每种字符的数量和值。
1 -> 1个1，即11。
11 -> 2个1，即21。
21 -> 1个2，1个1，即1211。以此类推。
Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
题目其实就是实现Java中String的indexOf函数。因此，直接调用该方法，显然是不合适的。
Given an array and a value, remove all instances of that value in place and return the new length.
Do not allocate extra space for another array, you must do this in place with constant memory.
The order of elements can be changed. It doesn’t matter what you leave beyond the new length.
Example: Given input array nums = [3,2,2,3], val = 3
Your function should return length = 2, with the first two elements of nums being 2.
跟从排好序的队列出移除重复元素问题类似。从给定的队列中移除给定的元素。最后，都需要把剩余的有效元素放在队列的开头，可以理解为同一个问题。
Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.
Do not allocate extra space for another array, you must do this in place with constant memory.
For example, Given input array nums = [1,1,2],
Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn’t matter what you leave beyond the new length.
题目其实包含两部分要求。首先，需要返回一个已排序数组，值不相同的元素的个数。例如：[1,1,2]返回2。这也是题目代码可以自动校验的部分。另一个隐含的要求是，要求不使用新的空间，并且在算出个数n后，将值不相同的元素，依次放置到数组的前N位。
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
即合并两个已经排好序的链表。并且要求返回的新链表是由原两个链表元素组合而成的。链表的结构定义也已经固定给出：
public class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
}
}
Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid.
The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.
即判断一个只包含括号的字符串，是不是合法的。
Write a function to find the longest common prefix string amongst an array of strings.
就是找出一个字符串数组中元素，最长的通用前缀。例如：{“ab”,”abc”,”abd”}，答案是 “ab”。