* Total Accepted: **106670**
  * Total Submissions: **329718**
  * Difficulty: **Medium**
  * Contributor: **LeetCode**

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the …

In LLP world, there is a hero called Teemo and his attacking can make his enemy Ashe be in poisoned condition. Now, given the Teemo’s attacking ascending time series towards Ashe and the poisoning time duration per Teemo’s attacking, you need to output the total time that Ashe is in poisoned condition.

You …

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?

思路：还是一个映射，如果某个位置要映射的时候已经为负了，就说明之前映射过该位置，那么该位置对应的元素就是出现了两个的元素。

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up: Could you do this in-place?

题意：给一个n*n的方阵，要求顺时针旋转90度。

思路：(x,y)->(y,n-1-x);

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

思路：。。。再次让我回想起高一的暑假。。。。

 1/* ***********************************************
 2Author :111qqz
 3Created Time :2017年04月11日 星期二 19时42分05秒
 4File Name :54.cpp
 5************************************************ */
 6 …

Given a collection of intervals, merge all overlapping intervals.

For example, Given [1,3],[2,6],[8,10],[15,18], return [1,6],[8,10],[15,18].

思路:dp[i]表示能否到达位置i…无脑dp即可。。。

1/* ***********************************************
2Author :111qqz
3Created Time :2017年04月11日 星期二 19时33分51秒
4File Name :55.cpp
5 …

Given a collection of intervals, merge all overlapping intervals.

For example, Given [1,3],[2,6],[8,10],[15,18], return [1,6],[8,10],[15,18].

思路：扫一遍即可。。

 1/* ***********************************************
 2Author :111qqz
 3Created Time :2017年04月11日 星期二 19时15分30秒
 4File Name :56.cpp
 5 …

Given an integer n, generate a square matrix filled with elements from 1 to _n_2 in spiral order.

思路：仿佛回到高一的那个暑假。。。

1/* ***********************************************
2Author :111qqz
3Created Time :2017年04月11日 星期二 18时52分15秒
4File Name :59.cpp
5************************************************ */
6class Solution {
7
8 …

Follow up for “Unique Paths”:

Now consider if some obstacles are added to the grids. How many unique paths would there be?

An obstacle and empty space is marked as 1 and 0 respectively in the grid.

For example,

There is one obstacle in the middle of a 3x3 grid as illustrated below.

1[
2  [0,0,0],
3  [0,1,0 …

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

数字三角形。。。。从坐上到右下问最短路径。。每次只能向下或者向右。。。

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

**Follow up:**Did you use extra space? A straight forward solution using O(m__n) space is probably a bad idea. A simple improvement uses O(m + n) space, but still not the best solution. Could you …

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up: Could you solve it with constant space complexity? (Note: …

Given a 2D board and a word, find if the word exists in the grid.

The word can be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.

思路：dfs即可。记得要回溯一下…

1/* …

Follow up for “Remove Duplicates”: What if duplicates are allowed at most twice?

For example, Given sorted array nums = [1,1,1,2,2,3],

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3. It doesn’t matter what you leave beyond the new length.

Subscribe …

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).

Write a function to determine if a given target is in the array.

The array may contain duplicates.

好像阿里一面的时候问过。。。

思路：肯定是二分。。。不过由于有重复元素。。。所以很恶心。。。

According to the Wikipedia’s article: “The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970.”

Given a board with m by n cells, each cell has an initial state live (1) or dead (0). Each cell interacts with its eight …

Given a collection of integers that might contain duplicates, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example, If nums = [1,2,2], a solution is:

1[
2  [2],
3  [1],
4  [1,2,2],
5  [2,2],
6  [1,2],
7  []
8]

思路：

复习（？）一下 枚举子集的三种写法

（还有种更飘逸的…先不写了orz

/* ***********************************************

 1Author :111qqz
 2Created Time :2017年04月05日 星期三 16时49分57秒
 3File Name :106.cpp
 4************************************************ */
 5/**
 6 * Definition for a binary tree node.
 7 * struct TreeNode {
 8 *     int val;
 9 *     TreeNode *left;
10 *     TreeNode * …

Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

Note:

  1. You **must not** modify the array (assume the array is read only).
  2. You must use …

Given an array of integers and an integer k, you need to find the number of unique k-diff pairs in the array. Here a k-diff pair is defined as an integer pair (i, j), where i and j are both numbers in the array and their absolute difference is k.

Example 1:

1Input: [3, 1, 4, 1, 5], k = 2
2Output: 2
3Explanation: There …