Ruizhi Ma's Blog

Problem 70

Climbing Stairs

问题描述 You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Note: Given n will be a ...

Posted by Ruizhi Ma on June 22, 2019

Problem 101

Symmetric Tree

问题描述 Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). （树状图画不出来，右转看原题：https://leetcode.com/problems/symmetric-tree/） Note: Bonus points if you could s...

Posted by Ruizhi Ma on June 21, 2019

Problem 66

Plus One

问题描述 Given a non-empty array of digits representing a non-negative integer, plus one to the integer. The digits are stored such that the most significant digit is at the head of the list, and each...

Posted by Ruizhi Ma on June 20, 2019

Problem 258

Add Digits

问题描述 Given a non-negative integer num, repeatedly add all its digits until the result has only one digit. Example: Input: 38 Output: 2 Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2. ...

Posted by Ruizhi Ma on June 20, 2019

Problem 167

Two Sum II - Input array is sorted

问题描述 Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two ...

Posted by Ruizhi Ma on June 19, 2019

递归

汉诺塔问题

解决思路所有不管多少个盘子，都可以看成两个盘子，即最后一个盘子，和其他所有盘子，然后都可以拆解为三步：将最后一个盘子上面的所有盘子，借助目标柱移动到中间柱子上将最后一个盘子移动到目标柱上将中间柱上所有盘子，借助初始柱，移动到最后一个柱子上 TestHanoi类 package demo3; public class TestHanoi { /* * n...

Posted by Ruizhi Ma on June 18, 2019

递归

斐波那契数列问题

TestFeobnacci类 package demo3; public class TestFebonacci { //斐波那契数列： 1 1 2 3 5 8 13 ... public static int febonacci(int i){ //出口条件 if(i == 1 || i == 2){ return 1; }else{ ...

Posted by Ruizhi Ma on June 18, 2019

Problem 125

Valid Palindrome

问题描述 Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. Note: For the purpose of this problem, we define empty string as valid palindrome...

Posted by Ruizhi Ma on June 18, 2019

Problem 387

First Unique Character in a String

问题描述 Given a string, find the first non-repeating character in it and return it’s index. If it doesn’t exist, return -1. Examples: s = “leetcode” return 0. s = “loveleetcode”, return 2. Note: Yo...

Posted by Ruizhi Ma on June 17, 2019

Problem 28

Implement strStr()

问题描述 Implement strStr(). Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Example 1: Input: haystack = “hello”, needle = “ll” Output: 2 Ex...

Posted by Ruizhi Ma on June 16, 2019

Ruizhi Ma's Blog

Problem 70

Climbing Stairs

Problem 101

Symmetric Tree

Problem 66

Plus One

Problem 258

Add Digits

Problem 167

Two Sum II - Input array is sorted

递归

汉诺塔问题

递归

斐波那契数列问题

Problem 125

Valid Palindrome

Problem 387

First Unique Character in a String

Problem 28

Implement strStr()

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