• 【CodeWars】Large Factorials (计算阶乘)


    JS数据位数限制:https://www.cnblogs.com/wangmeijian/p/9217352.html
    使用数组实现阶乘运算的过程:https://www.cnblogs.com/hiluna/p/8868175.html

    JavaScript中的基本数据类Number是双精度浮点数,它可以表示的最大安全范围是正负9007199254740991,也就是2的53次方减一

    CodeWars里的要求是不用JS提供的bigInt等数据类型,也不能使用其他插件

    题目:
    In mathematics, the factorial of integer n is written as n!. It is equal to the product of n and every integer preceding it. For example: 5! = 1 x 2 x 3 x 4 x 5 = 120

    Your mission is simple: write a function that takes an integer n and returns the value of n!.

    You are guaranteed an integer argument. For any values outside the non-negative range, return null, nil or None (return an empty string "" in C and C++). For non-negative numbers a full length number is expected for example, return 25! = "15511210043330985984000000" as a string.

    For more on factorials, see http://en.wikipedia.org/wiki/Factorial

    NOTES:

    The use of BigInteger or BigNumber functions has been disabled, this requires a complex solution

    I have removed the use of require in the javascript language.

    答案:

    function factorial(n){
      if(n<0){return null;}
      if(n==0 ||n==1){return "1";}
      let arr=[1];
      let temp=0; 
      for(let i=2; i<=n; i++){                                //取出2~n之间的数字
        for(let j=0,prior=0; j<arr.length ||prior!=0; j++){   //从个位数arr[0]开始相乘(有的时候进位的数字要放入arr[length+1],要增加一个判断条件prior!=0)
          temp = (j<arr.length)? arr[j]*i+prior : prior;      //temp存储相乘结果(记得加上prior)
          arr[j] = temp%10;                                   //更新当前位arr[j]
          prior= (temp-arr[j])/10;                            //算出进位
        }
      }
      return arr.reverse().join("");
    }
    
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  • 原文地址:https://www.cnblogs.com/hikki-station/p/13791448.html
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