Project-Euler-020|euler-multilingual

Problem


$n!$ means $n \times (n - 1) \times … \times 3 \times 2 \times 1$.

Find the sum of the digits in the number $100!$.

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Simple Implement of Spring MVC|Java

简单模拟Spring MVC

在Spring MVC中，将一个普通的java类标注上Controller注解之后，再将类中的方法使用RequestMapping注解标注，那么这个普通的java类就够处理Web请求，示例代码如下：

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/**
 * 使用Controller注解标注LoginUI类
 */
@Controller
public class LoginUI {
    
    //使用RequestMapping注解指明forward1方法的访问路径  
    @RequestMapping("LoginUI/Login2")
    public View forward1(){
        //执行完forward1方法之后返回的视图
        return new View("/login2.jsp");  
    }
    
    //使用RequestMapping注解指明forward2方法的访问路径  
    @RequestMapping("LoginUI/Login3")
    public View forward2(){
        //执行完forward2方法之后返回的视图
        return new View("/login3.jsp");  
    } 
}

spring通过java annotation就可以注释一个类为action ，在方法上添加上一个java annotation 就可以配置请求的路径了，那么这种机制是如何实现的呢，今天我们使用”自定义注解+Servlet”来简单模拟一下Spring MVC中的这种注解配置方式。

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LeetCode Notes 020|leetcode-javascript

Count of Range Sum

Given an integer array nums, return the number of range sums that lie in [lower, upper] inclusive.
Range sum S(i, j) is defined as the sum of the elements in nums between indices i and j (i ≤ j), inclusive.

Note:
A naive algorithm of $O(n^2)$ is trivial. You MUST do better than that.

Example:
Given nums = [-2, 5, -1], lower = -2, upper = 2,

Return 3.
The three ranges are : [0, 0], [2, 2], [0, 2] and their respective sums are: -2, -1, 2.

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LeetCode Notes 019|leetcode-javascript

Count And Say

The count-and-say sequence is the sequence of integers with the first five terms as following:

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1.     1
2.     11
3.     21
4.     1211
5.     111221

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer $n$, generate the $n^th$ term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

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Input: 1
Output: "1"

Example 2:

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Input: 4
Output: "1211"

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LeetCode Notes 018|leetcode-javascript

Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

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Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

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LeetCode Notes 017|leetcode-javascript

Continuous Subarray Sum

Given a list of non-negative numbers and a target integer k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to the multiple of k, that is, sums up to n*k where n is also an integer.

Example 1:

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Input: [23, 2, 4, 6, 7],  k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.

Example 2:

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Input: [23, 2, 6, 4, 7],  k=6
Output: True
Explanation: Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42.

Note:

  1. The length of the array won’t exceed 10,000.
  2. You may assume the sum of all the numbers is in the range of a signed 32-bit integer.
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