每日一道算法题 - KaprekarsConstant(hard-1)

虽然都是很简单的算法，每一个都只需5分钟左右，但写起来总会遇到不一样的小问题，但愿你们能跟我一块儿天天进步一点点。
更多的小算法练习，能够查看个人文章。

规则

Using the JavaScript language, have the function KaprekarsConstant(num) take the num parameter being passed which will be a 4-digit number with at least two distinct digits. Your program should perform the following routine on the number: Arrange the digits in descending order and in ascending order (adding zeroes to fit it to a 4-digit number), and subtract the smaller number from the bigger number. Then repeat the previous step. Performing this routine will always cause you to reach a fixed number: 6174. Then performing the routine on 6174 will always give you 6174 (7641 - 1467 = 6174). Your program should return the number of times this routine must be performed until 6174 is reached. For example: if num is 3524 your program should return 3 because of the following steps: (1) 5432 - 2345 = 3087, (2) 8730 - 0378 = 8352, (3) 8532 - 2358 = 6174.

使用JavaScript语言，让函数KaprekarsConstant（num）获取 传递的num参数，该参数将是一个4位数字，至少有两个不一样的数字。
按降序和升序排列数字（添加零以使其适合4位数字），用较大的数字减去较小的数字。
而后重复上一步，直到相减结果等于固定数字：6174，返回该程序必须执行的次数。
例如：若是传入的参数为3524，你的程序应该返回3，即该程序必须执行3次才能获得6174的结果。
由于如下步骤：（1）5432 - 2345 = 3087，（2）8730 - 0378 = 8352，（3）8532 - 2358 = 6174.

function KaprekarsConstant(num) { 

  // code goes here  
  return num; 
}
   
// keep this function call here 
KaprekarsConstant(3524);

测试用例

Input:2111
Output:5

Input:9831
Output:7

my code

function KaprekarsConstant(num) {
  var count = 0
  while (true) {
    var maxNum = num
      .toString()
      .split('')
      .sort((item1, item2) => item2 - item1)
      .join('')
    maxNum = Number(maxNum)

    var minNum = num
      .toString()
      .split('')
      .sort()
      .join('')
    minNum = Number(minNum)

    num = '0000' + (maxNum - minNum)
    num = num.substr(-4)
    count++

    if (num == 6174 || num == 0) break
  }

  return count
}

other code

code-1

function KaprekarsConstant(num) {
    const KAP = 6174;
    var count = 0;
    while (true) {
        var num = evaluator(num)
        if (num === true) {
            return count;
        }
    }

    function evaluator(num) {
        count++
        console.log('count', count);
        var minNumArr = num.toString().split('').sort();
        var maxNumArr = minNumArr.slice(0).reverse();
        var littleNum = parseInt(minNumArr.join(''), 10);
        var bigNum = parseInt(maxNumArr.join(''), 10);
        while (bigNum < 1000) {
            bigNum = bigNum * 10;
        }

        return bigNum - littleNum === KAP ? true : bigNum - littleNum;
    }
}

code-2

function KaprekarsConstant(num) {
  var count = 0;
  while (num != 6174) {
    count += 1;
    var numArr = num.toString().split('');
    while (d.length < 4) {
      numArr.push('0');
    }
    var smaller = numArr.sort().join('');
    var bigger = numArr.reverse().join('');
    num = bigger - smaller;
  }
  return count;
}

code-3

function KaprekarsConstant(num) { 

    let count = 0;
    while (num != 6174) {
        let numArray = num.toString().split('').sort();
        
        let ascending = parseInt(numArray.join(''));
        let descending = parseInt(numArray.reverse().join(''));
        
        while (descending.toString().length < 4) {
            descending *= 10;
        }
        
        num = Math.abs(ascending - descending);

        count++;
        if (count > 999) break;  // failover
    }

    return count;
}

思路

我的思路：

1. 本想使用递归去解决，代码量会更少更优雅，而后发现须要计算执行的次数，因此才使用while去遍历执行（其实使用闭包也能够解决，无奈题目调用就是KaprekarsConstant(xxxx)）
2. 先把数字转成字符串再转数组，使用数组升降排序拿到最大最小值，相减以后获得结果
3. 给相减结果补0，保证相减结果一直都是4位数
4. 当相减结果等于6174或0时，中断while循环，返回执行次数

优化点：
1.minArr = num.toString().split('').sort(); minNum = minArr.join("")，那么maxNum能够直接使用minArr.reverse().join('')获得
2.能够把if判断内容放到while上
3.补0可使用 num * 10 的方式，而不是字符串补零