最让你恶心痛苦的那些人，你必要从他们身上学到最重要和有用的东西。 所有的痛苦都不能白受，克我者必生我。

在知乎看到这句话，不禁在想

人无疑是zhangk，可是学到了什么呢？

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array …

Find the contiguous subarray within an array (containing at least one number) which has the largest product.

For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest product = 6.

思路：由于有正，有负，还有0.。。所以比最大子串之和要复杂一些。。。

dp[i].max表示到当前位置的最大乘积。

Given a sorted integer array without duplicates, return the summary of its ranges.

For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].

题意：把连续的数连续表示

思路：模拟。注意有负数，注意有-2147483648这种数据。

本来还想着，可能是leetcode加数据的审核机制太松，导致被人加了奇怪的数据。。。

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s. If there isn’t one, return 0 instead.

For example, given the array [2,3,1,2,4,3] and s = 7, the subarray [4,3] has the minimal length under the problem constraint

思路：尺取即可。。好久没写，竟然 …

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

题意：给你n个数，要求找出出现此处大于n/3的。。。

思路：之前做过一个找出n个数出现此处大于n/2的题目，思想是“非吾族类，其心必异”。。

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

题意：一个数组，由0,1,2组成，现在要求升序排列

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 two lines, which together with x-axis forms a container, such that the container contains the most water.

Note: You may …

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

思路： 排序，然后two pointer,复杂度 O(n^2)

1/* ***********************************************
2Author :111qqz
3 …

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note: The solution set must not contain duplicate quadruplets.

思路： O(n^2)枚举两个元素，变成2-sum问题，总体复杂度O(n^3)

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

Note: The solution set must not contain duplicate triplets.

思路：排序O(nlgn)，然后枚举一个元素O(n),对于每个元素，在剩下的区间中 two pointer O(n)

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

题意：1..9个数，从中选择k个，和为n，要求输出所有满足题意的集合。

思路：枚举子集，根据sum和集合元素个数剪枝即可。

Given two integers n and k, return all possible combinations of k numbers out of 1 … n.

思路：就是枚举子集，根据集合的大小剪枝。。。最后只要集合大小为k的集合

 1/* ***********************************************
 2Author :111qqz
 3Created Time :2017年04月13日 星期四 15时25分37秒
 4File Name :77.cpp
 5************************************************ */
 6 …

The set [1,2,3,…,_n_] contains a total of n! unique permutations.

By listing and labeling all of the permutations in order, We get the following sequence (ie, for n = 3):

  1. `"123"`
  2. `"132"`
  3. `"213"`
  4. `"231"`
  5. `"312"`
  6. `"321"`

Given n …

Given a collection of numbers that might contain duplicates, return all possible unique permutations.__

思路：和leet code 46 类似，最后用set去个重即可。。

1/* ***********************************************
2Author :111qqz
3Created Time :2017年04月13日 星期四 15时00分48秒
4File Name :47.cpp
5************************************************ */
6 …

Given a collection of distinct numbers, return all possible permutations.

思路：调用n-1次 leetcode 31 解题报告 中提到的算法即可。。。

1/* ***********************************************
2Author :111qqz
3Created Time :2017年04月13日 星期四 14时49分34秒
4File Name :46.cpp
5 ************************************************ */
6class Solution {
7
8 …

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some …

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

思路：找规律。。。二分。。。

Given an array of integers sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm’s runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

For example, Given [5, 7, 7, 8, 8, 10] and target value 8, return [3, …

Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

  * All numbers (including target) will be positive integers.
  * The solution set …