本文基于免费代码营基本算法脚本“分解数字”
在数学中，非负整数n的阶乘可能是一个棘手的算法。在本文中，我将解释这种方法，首先使用递归函数，第二种使用而循环，第三种使用以循环。
算法挑战
返回提供的整体的阶乘。
如果整体用字母n表示，则阶乘是所有小于或等于n的正整数的乘积。
阶乘经常用简写符号n！表示！
例如：5！= 1 * 2 * 3 * 4 * 5 = 120
|
1
2
3
4
|
function factorialize(num) {
return num;
}
factorialize(5);
|
提供的测试用例
- factorialize（0）应该返回1
- factorialize（5）应该返回120
- factorialize（10）应该返回3628800
- factorialize（20）应该返回2432902008176640000
什么是因数分解？
当将一个因数分解时，就是称为数字乘以每个连续的数字减一个。
如果您的电话号码是5，则您将：
5! = 5 * 4 * 3 * 2 * 1
该模式为：
0! = 1
1! = 1
2! = 2 * 1
3! = 3 * 2 * 1
4! = 4 * 3 * 2 * 1
5! = 5 * 4 * 3 * 2 * 1
1.递归分解一个数字
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
function factorialize(num) {
// If the number is less than 0, reject it.
if (num < 0)
return -1;
// If the number is 0, its factorial is 1.
else if (num == 0)
return 1;
// Otherwise, call the recursive procedure again
else {
return (num * factorialize(num - 1));
/*
First Part of the recursion method
You need to remember that you won't have just one call, you'll have several nested calls
Each call: num === "?" num * factorialize(num - 1)
1st call – factorialize(5) will return 5 * factorialize(5 - 1) // factorialize(4)
2nd call – factorialize(4) will return 4 * factorialize(4 - 1) // factorialize(3)
3rd call – factorialize(3) will return 3 * factorialize(3 - 1) // factorialize(2)
4th call – factorialize(2) will return 2 * factorialize(2 - 1) // factorialize(1)
5th call – factorialize(1) will return 1 * factorialize(1 - 1) // factorialize(0)
Second part of the recursion method
The method hits the if condition, it returns 1 which num will multiply itself with
The function will exit with the total value
5th call will return (5 * (5 - 1)) // num = 5 * 4
4th call will return (20 * (4 - 1)) // num = 20 * 3
3rd call will return (60 * (3 - 1)) // num = 60 * 2
2nd call will return (120 * (2 - 1)) // num = 120 * 1
1st call will return (120) // num = 120
If we sum up all the calls in one line, we have
(5 * (5 - 1) * (4 - 1) * (3 - 1) * (2 - 1)) = 5 * 4 * 3 * 2 * 1 = 120
*/
}
}
factorialize(5);
|
没有注释：
|
1
2
3
4
5
6
7
8
9
10
|
function factorialize(num) {
if (num < 0)
return -1;
else if (num == 0)
return 1;
else {
return (num * factorialize(num - 1));
}
}
factorialize(5);
|
2.用WHILE循环分解一个数字
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
function factorialize(num) {
// Step 1. Create a variable result to store num
var result = num;
// If num = 0 OR num = 1, the factorial will return 1
if (num === 0 || num === 1)
return 1;
// Step 2. Create the WHILE loop
while (num > 1) {
num--; // decrementation by 1 at each iteration
result = result * num; // or result *= num;
/*
num num-- var result result *= num
1st iteration: 5 4 5 20 = 5 * 4
2nd iteration: 4 3 20 60 = 20 * 3
3rd iteration: 3 2 60 120 = 60 * 2
4th iteration: 2 1 120 120 = 120 * 1
5th iteration: 1 0 120
End of the WHILE loop
*/
}
// Step 3. Return the factorial of the provided integer
return result; // 120
}
factorialize(5);
|
没有注释：
|
1
2
3
4
5
6
7
8
9
10
11
|
function factorialize(num) {
var result = num;
if (num === 0 || num === 1)
return 1;
while (num > 1) {
num--;
result *= num;
}
return result;
}
factorialize(5);
|
3.使用FOR循环分解数字
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
|
function factorialize(num) {
// If num = 0 OR num = 1, the factorial will return 1
if (num === 0 || num === 1)
return 1;
// We start the FOR loop with i = 4
// We decrement i after each iteration
for (var i = num - 1; i >= 1; i--) {
// We store the value of num at each iteration
num = num * i; // or num *= i;
/*
num var i = num - 1 num *= i i-- i >= 1?
1st iteration: 5 4 = 5 - 1 20 = 5 * 4 3 yes
2nd iteration: 20 3 = 4 - 1 60 = 20 * 3 2 yes
3rd iteration: 60 2 = 3 - 1 120 = 60 * 2 1 yes
4th iteration: 120 1 = 2 - 1 120 = 120 * 1 0 no
5th iteration: 120 0 120
End of the FOR loop
*/
}
return num; //120
}
factorialize(5);
|
没有注释：
|
1
2
3
4
5
6
7
8
9
|
function factorialize(num) {
if (num === 0 || num === 1)
return 1;
for (var i = num - 1; i >= 1; i--) {
num *= i;
}
return num;
}
factorialize(5);
|
到此这篇关于详解JavaScript中分解数字的三种方法的文章就介绍到这了,更多相关js分解数字内容请搜索服务器之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持服务器之家！
原文链接：https://blog.csdn.net/qq_25879801/article/details/111332992