Ruizhi Ma's Blog

Keep Calm and Carry On

Problem 112

Sum Path

问题描述 见链接：https://leetcode.com/problems/path-sum/ 解决思路 其实就是深度优先（DFS），不断递归左右子树。 代码 package leetcode; public class PathSum { public class TreeNode { int val; TreeNode left; ...

Posted by Ruizhi Ma on June 29, 2019

Problem 102

Binary Tree Level Order Traversal

问题描述 题目看链接：https://leetcode.com/problems/binary-tree-level-order-traversal/ 解决思路 同Pro107 代码 /** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode le...

Posted by Ruizhi Ma on June 27, 2019

Problem 171

Excel Sheet Column Number

问题描述 Given a column title as appear in an Excel sheet, return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: ...

Posted by Ruizhi Ma on June 26, 2019

Problem 169

Majority Element

问题描述 Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times. You may assume that the array is non-empty and the majority elem...

Posted by Ruizhi Ma on June 26, 2019

Problem 136

Single Number

问题描述 Given a non-empty array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it wi...

Posted by Ruizhi Ma on June 25, 2019

Problem 119

Pascal's Triangle II

问题描述 题目看链接：https://leetcode.com/problems/pascals-triangle-ii/ 解决思路 这题除了题目和118有略微不同，只需要返回最后一行，还有就是需要在O(n)空间完成，虽然118虽然改一下就能出结果，但那个是O(n^2)。其实杨辉三角有一个公式，即第n行的m个数可表示为 C(n-1,m-1).这样就很简单了，算出第n行第一个数，然后遍历该行...

Posted by Ruizhi Ma on June 25, 2019

Problem 118

Pascal's Triangle

问题描述 其实就是杨辉三角，题目看网址：https://leetcode.com/problems/pascals-triangle/ 解决思路 主要有几个地方需要处理： 通过遍历上一行元素，将当前元素由其左上角和右上角元素之和获得 每行最后一个元素1，要单独加入 要使用双层List(List<List<>>),内层List是每一行所有元素的集合，外层...

Posted by Ruizhi Ma on June 25, 2019

HashMap

手动实现HaspMap的常用方法

Node3类 package cn.sxt.myCollection; /* * to be used in SxtHashMap */ public class Node3<K,V> { int hash; K key; V value; Node3 next; } SxtHashMap04类 package cn.sxt.myCollection;...

Posted by Ruizhi Ma on June 25, 2019

StringBuilder和StringBuffer

可变序列，常用方法，效率探究

TestStringBuilder类 package commonClass; /** * Test StringBuilder, StringBuffer variable character sequence * @author Sober * */ public class TestStringBuilder { public static void main(Stri...

Posted by Ruizhi Ma on June 25, 2019

Problem 67

Add Binary

问题描述 Given two binary strings, return their sum (also a binary string). The input strings are both non-empty and contains only characters 1 or 0. Example 1: Input: a = “11”, b = “1” Output: “100...

Posted by Ruizhi Ma on June 24, 2019

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