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Posts published in January 2018

花花酱 LeetCode 282. Expression Add Operators

题目大意:给你一个字符串,让你在数字之间加上+,-,*使得等式的值等于target。让你输出所有满足条件的表达式。

Given a string that contains only digits 0-9 and a target value, return all possibilities to add binary operators (not unary) +-, or * between the digits so they evaluate to the target value.

Examples:

Slides:

 

Solution 1: DFS

Time complexity: O(4^n)

Space complexity: O(n^2) -> O(n)

C++

C++ / SC O(n)

Java

花花酱 LeetCode 480. Sliding Window Median

题目大意:让你求移动窗口的中位数。

Problem:

Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two middle value.

Examples:

[2,3,4] , the median is 3

[2,3], the median is (2 + 3) / 2 = 2.5

Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Your job is to output the median array for each window in the original array.

For example,
Given nums = [1,3,-1,-3,5,3,6,7], and k = 3.

Therefore, return the median sliding window as [1,-1,-1,3,5,6].

Note: 
You may assume k is always valid, ie: k is always smaller than input array’s size for non-empty array.

 

Solution 0: Brute Force

Time complexity: O(n*klogk) TLE 32/42 test cases passed

Solution 1: Insertion Sort

Time complexity: O(k*logk +  (n – k + 1)*k)

Space complexity: O(k)

C++ / vector

C++ / vector + binary_search for deletion.

Java

Java / Binary Search

 

Python

Solution 2: BST

 

Related Problems:

花花酱 LeetCode 763. Partition Labels

题目大意:把字符串分割成尽量多的不重叠子串,输出子串的长度数组。要求相同字符只能出现在一个子串中。

Problem:

A string S of lowercase letters is given. We want to partition this string into as many parts as possible so that each letter appears in at most one part, and return a list of integers representing the size of these parts.

Example 1:

Solution 0: Brute Force

Time complexity: O(n^2)

Space complexity: O(1)

C++

Python

 

Solution 1: Greedy

Time complexity: O(n)

Space complexity: O(26/128)

C++

Java

Python3

 

花花酱 LeetCode 239. Sliding Window Maximum

题目大意:给你一个数组,让你输出移动窗口的最大值。

Problem:

https://leetcode.com/problems/sliding-window-maximum/

Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position.

For example,
Given nums = [1,3,-1,-3,5,3,6,7], and k = 3.

Therefore, return the max sliding window as [3,3,5,5,6,7].

Note: 
You may assume k is always valid, ie: 1 ≤ k ≤ input array’s size for non-empty array.

Follow up:
Could you solve it in linear time?

 

Idea:

 

Solution 1: Brute Force

Time complexity: O((n – k + 1) * k)

Space complexity: O(1)

C++

Java

Python

Solution 2: BST

Time complexity: O((n – k + 1) * logk)

Space complexity: O(k)

C++

Solution 3: Monotonic Queue

Time complexity: O(n)

Space complexity: O(k)

C++

C++ V2

C++ V3

Java

Python3

Python3 V2

花花酱 LeetCode 762. Prime Number of Set Bits in Binary Representation

题目大意:求给定范围内,数的二进制形式中1的个数为素数个的数字的个数。

Given two integers L and R, find the count of numbers in the range [L, R] (inclusive) having a prime number of set bits in their binary representation.

(Recall that the number of set bits an integer has is the number of 1s present when written in binary. For example, 21 written in binary is 10101 which has 3 set bits. Also, 1 is not a prime.)

Example 1:

Example 2:

Note:

  1. L, R will be integers L <= R in the range [1, 10^6].
  2. R - L will be at most 10000.

Solution 1: Brute Force

C++

 

 

Java

Python2

Python2