Ruizhi Ma's Blog

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Problem 198

House Robber

问题描述 You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjace...

Posted by Ruizhi Ma on July 8, 2019

Problem 157

Read N Characters Given Read4

问题描述 The API: int read4(char *buf) reads 4 characters at a time from a file. The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left ...

Posted by Ruizhi Ma on July 8, 2019

HashSet

HashSet底层实现

# package cn.sxt.myCollection; import java.util.HashMap; import java.util.HashSet; import java.util.Map; import java.util.Set; public class SxtHashSet { HashMap map; private static final O...

Posted by Ruizhi Ma on July 8, 2019

HashSet

HashSet的基本用法

TestHashMap类 package cn.sxt.collection; import java.util.HashSet; import java.util.Set; /* * 测试HashSet的基本用法 * Set没有顺序，不可重复 * List有顺序，可重复 */ public class TestHashSet { public static void ma...

Posted by Ruizhi Ma on July 8, 2019

Problem 191

Number of 1 Bits

问题描述 Write a function that takes an unsigned integer and return the number of ‘1’ bits it has (also known as the Hamming weight). Example 1: Input: 00000000000000000000000000001011 Output: 3 Exp...

Posted by Ruizhi Ma on July 7, 2019

Problem 190

Reverse Bits

问题描述 Reverse bits of a given 32 bits unsigned integer. Example 1: Input: 00000010100101000001111010011100 Output: 00111001011110000010100101000000 Explanation: The input binary string 00000010...

Posted by Ruizhi Ma on July 7, 2019

Problem 170

Two Sum III Data Structure Design

问题描述 Design and implement a TwoSum class. It should support the following operations: add and find. add - Add the number to an internal data structure. find - Find if there exists any pair of num...

Posted by Ruizhi Ma on July 7, 2019

Problem 172

Factorial Trailing Zeros

问题描述 Given an integer n, return the number of trailing zeroes in n!. Example 1: Input: 3 Output: 0 Explanation: 3! = 6, no trailing zero. Example 2: Input: 5 Output: 1 Explanation: 5! = 120...

Posted by Ruizhi Ma on July 5, 2019

Problem 195

Tenth Line

问题描述 Given a text file file.txt, print just the 10th line of the file. Example: Assume that file.txt has the following content: Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Li...

Posted by Ruizhi Ma on July 4, 2019

Problem 183

Customers Who Never Order

问题描述 https://leetcode.com/problems/customers-who-never-order/ 解决思路 用LEFT JOIN通过ON的条件，将两个表连接，筛选出tb2中Id为空的，即为答案。 问题解惑 ON和WHERE的区别？ ON是连接条件；WHERE是筛选条件 代码 # Write your MySQL query statement below SE...

Posted by Ruizhi Ma on July 4, 2019

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