Codewars-Javascript训练手册：数组（上）

「爱情、让人受尽委屈。」 2022-08-21 05:53 150阅读 0赞

## Directions Reduction ##

### **题目描述(Description)：** ###

write a function dirReduc which will take an array of strings and returns an array of strings with the needless directions removed (W<->E or S<->N side by side).  
In \[“NORTH”, “EAST”, “WEST”, “SOUTH”, “WEST”, “WEST”\], “NORTH” and “SOUTH” are not directly opposite but they become directly opposite after the reduction of “EAST” and “WEST” so the whole path is reducible to \[“WEST”, “WEST”\].  
只有相邻以及抵消后相邻的的两个相反方向可以抵消

### 题目注解(Note)： ###

All paths can’t be made simpler. The path \[“NORTH”, “WEST”, “SOUTH”, “EAST”\] is not reducible. “NORTH” and “WEST”, “WEST” and “SOUTH”, “SOUTH” and “EAST” are not directly opposite of each other and can’t become such. Hence the result path is itself : \[“NORTH”, “WEST”, “SOUTH”, “EAST”\].

### **Solution:** ###

#### 某论坛大神的解决方案 ####

直达[地址][Link 1]

#### **Codewars**排名最高的答案： ####

### 知识点： ###

`splice()` 方法：向/从数组中添加/删除项目，然后返回被删除的项目(新的数组)。

注释：该方法会改变原始数组。  
**语法**

> arrayObject.splice(index,howmany,item1,…..,itemX)

splice() 方法与 slice() 方法的作用是不同的，splice() 方法会直接对数组进行修改。参考[链接][Link 2]  
`reduce (Array)` (JavaScript)方法：对数组中的所有元素调用指定的回调函数。该回调函数的返回值为累积结果，并且此返回值在下一次调用该回调函数时作为参数提供。  
**语法**

> array1.reduce(callbackfn\[, initialValue\])

返回值为通过最后一次调用回调函数获得的累积结果。参考[链接][Link 3]

## Tribonacci Sequence(类斐波那契数列) ##

### **题目描述** ###

create a fibonacci function that given a signature array/list, returns the first n elements - signature included of the so seeded sequence.  
Signature will always contain 3 numbers; n will always be a non-negative number; if n==0, then return an empty array and be ready for anything else which is not clearly specified ;)  
数组Signature 总包含3个数值，n为非负整数，当n=0的时候，返回一个空数组。

### **Soluation:** ###

Codewars 得票最高的答案：

function tribonacci(signature,n){   
      for (var i = 0; i < n-3; i++) { // iterate n times
        signature.push(signature[i] + signature[i+1] + signature[i+2]); // add last 3 array items and push to trib
      }
      //优化算法，去掉了if语句。
      return signature.slice(0, n); //return trib - length of n
    }

这就是与高手之间的差距啊。

[Link 1]: http://www.stage1st.com/2b/forum.php?mod=viewthread&tid=1162418
[Link 2]: http://www.w3school.com.cn/jsref/jsref_splice.asp
[Link 3]: https://msdn.microsoft.com/library/ff679975%28v=vs.94%29.aspx