Leetcode on 111qqz's blog

2020年终总结

Sun, 03 Jan 2021 16:54:57 +0800

本来不知道写什么所以不打算写了，不过后来觉得可以把今年做的一些重大的决定写出来，把当时的分析和想法记录下来。这样若干年后再回看，就能找到，是哪些明智或愚蠢的决定，对人生产生了巨大的影响。

leetcode162. Find Peak Element (O(lgn)复杂度寻找峰值)

Fri, 14 Apr 2017 12:25:16 +0000

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.

leetcode 152. Maximum Product Subarray (最大连续子序列乘积，dp)

Fri, 14 Apr 2017 11:33:30 +0000

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.

leetcode 228. Summary Ranges

Fri, 14 Apr 2017 10:51:39 +0000

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

leetcode 209. Minimum Size Subarray Sum (尺取法)

Thu, 13 Apr 2017 13:50:02 +0000

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.

leetcode 229. Majority Element II （O(1)空间找出现次数大于n/3的元素）

Thu, 13 Apr 2017 12:41:33 +0000

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。。。

leetcode 75. Sort Colors

Thu, 13 Apr 2017 12:02:02 +0000

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.

leetcode 11. Container With Most Water (two pointer)

Thu, 13 Apr 2017 10:13:01 +0000

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.

leetcode 16. 3Sum Closest (k-sum问题，two pointer)

Thu, 13 Apr 2017 09:45:45 +0000

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.

leetcode 18. 4Sum (k-sum问题，two pointer)

Thu, 13 Apr 2017 09:34:15 +0000

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.

leetcode 15. 3Sum (k-sum问题，two pointer)

Thu, 13 Apr 2017 08:21:52 +0000

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.

leetcode 216. Combination Sum III Add to List (枚举子集，限定集合大小，和为定值）

Thu, 13 Apr 2017 07:55:09 +0000

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.

leetcode 60. Permutation Sequence (求第k个排列)

Thu, 13 Apr 2017 07:24:41 +0000

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):

leetcode 47. Permutations II (生成全排列，有重复元素)

Thu, 13 Apr 2017 07:14:03 +0000

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。。

leetcode 46. Permutations (生成全排列，无重复元素)

Thu, 13 Apr 2017 06:59:43 +0000

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。。。

leetcode 31. Next Permutation (in-place 生成下一个全排列)

Thu, 13 Apr 2017 06:47:55 +0000

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).

leetcode 33. Search in Rotated Sorted Array (无重复数的旋转数组找定值)

Thu, 13 Apr 2017 06:29:37 +0000

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).

leetcode 34. Search for a Range (二分，找到一段值为tar的区间)

Thu, 13 Apr 2017 05:34:45 +0000

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).

leetcode 39. Combination Sum (dfs，求所有的组合，和为定值，每个数可以重复用)

Thu, 13 Apr 2017 02:47:49 +0000

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.

leetcode 40. Combination Sum II (枚举子集，和为定值)

Wed, 12 Apr 2017 16:23:29 +0000

 * 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.

leetcode 495. Teemo Attacking

Wed, 12 Apr 2017 16:00:57 +0000

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.

leetcode 442. Find All Duplicates in an Array（找出出现两次的元素）

Wed, 12 Apr 2017 15:21:23 +0000

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.

leetcode 48. Rotate Image (旋转方阵(in place))

Wed, 12 Apr 2017 13:22:33 +0000

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。

leetcode 54. Spiral Matrix (矩阵蛇形取数)

Tue, 11 Apr 2017 12:07:54 +0000

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。。。。

leetcode 55. Jump Game (dp)

Tue, 11 Apr 2017 11:39:15 +0000

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。。。

leetcode 56. Merge Intervals (模拟，求相交区间)

Tue, 11 Apr 2017 11:30:32 +0000

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************************************************ */
 6/**
 7
 8 * Definition for an interval.
 9
10 * struct Interval {
11
12 * int start;
13
14 * int end;
15
16 * Interval() : start(0), end(0) {}
17
18 * Interval(int s, int e) : start(s), end(e) {}
19
20 * };
21
22 */
23
24class Solution {
25
26public:
27
28 int n;
29 static bool cmp(Interval A,Interval B)
30 {
31	return A.start<B.start;
32 }
33 vector<Interval> merge(vector<Interval>& pi) {
34	vector<Interval>res;
35	n = pi.size();
36	if (n==0) return res;
37	sort(pi.begin(),pi.end(),cmp);
38	int l = -1,r = -1;
39	for ( int i = 0 ; i < n ; i++)
40	{
41	 if (l==-1&&r==-1)
42	 {
43		l = pi[0].start;
44		r = pi[0].end;
45		continue;
46	 }
47	 if (pi[i].start<=r)
48	 {
49		r = max(r,pi[i].end);
50		continue;
51	 }
52	 if (pi[i].start>r)
53	 {
54		res.push_back(Interval(l,r));
55		l = pi[i].start;
56		r = pi[i].end;
57		continue;
58	 }
59	}
60	//最后一组不要忘记
61	res.push_back(Interval(l,r));
62	int siz = res.size();
63	for ( int i = 0 ; i < siz ;i++) printf("%d ",res[i].start,res[i].end);
64
65
66 return res;
67
68 }
69
70};

leetocde 59. Spiral Matrix II (模拟)

Tue, 11 Apr 2017 11:07:52 +0000

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。。。

leetocde 63. Unique Paths II

Tue, 11 Apr 2017 10:50:57 +0000

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.

leetcode 64. Minimum Path Sum (二维dp)

Mon, 10 Apr 2017 02:35:20 +0000

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.

leetcode 73. Set Matrix Zeroes (矩阵置0，乱搞)

Mon, 10 Apr 2017 01:16:43 +0000

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 devise a constant space solution?

leetcode 238. Product of Array Except Self (乱搞)

Sun, 09 Apr 2017 11:50:05 +0000

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].

leetcode 79. Word Search (dfs)

Fri, 07 Apr 2017 06:59:26 +0000

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.

leetcode 80 Remove Duplicates from Sorted Array II （有序数组去除重复元素）

Wed, 05 Apr 2017 13:36:44 +0000

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.

leetcode 81. Search in Rotated Sorted Array II (有重复元素的旋转数组找给定值)

Wed, 05 Apr 2017 13:17:51 +0000

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).

leetcode 289. Game of Life (模拟)

Wed, 05 Apr 2017 12:03:28 +0000

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 neighbors (horizontal, vertical, diagonal) using the following four rules (taken from the above Wikipedia article):

leetcode 90. Subsets II (枚举子集)

Wed, 05 Apr 2017 10:45:02 +0000

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:

leetcode 287. Find the Duplicate Number (floyd判圈算法找重复元素)

Wed, 05 Apr 2017 07:31:49 +0000

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.

leetcode 532. K-diff Pairs in an Array （找差为k的数对）

Wed, 05 Apr 2017 06:53:02 +0000

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.

leetcode 448. Find All Numbers Disappeared in an Array(寻找所有消失的元素）

Wed, 05 Apr 2017 06:19:06 +0000

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

Find all the elements of [1, n] inclusive that do not appear in this array.