【5 kyu】Largest 5 digit number in a series

原题目

In the following 6 digit number:
283910
91 is the greatest sequence of 2 digits.

In the following 10 digit number:
1234567890
67890 is the greatest sequence of 5 digits.

Complete the solution so that it returns the largest five digit number found within the number given. The number will be passed in as a string of only digits. It should return a five digit integer. The number passed may be as large as 1000 digits.

题目：找出一个数值(该数值将以字符串的形式传入)中最大的五位数。

My Solution

• 若是数字的位数小于6，则直接返回该数值
• 若是数字的位数不小于六位，则依次截取连续的5位数，求取最大值

function solution(digits){
  if(digits < 100000) return Number(digits);
  
  var maxNum = digits.substr(0, 5);
  
  for(var i=1, l=digits.length - 4; i<l; i++) {
    maxNum = Math.max(maxNum, digits.substr(i, 5));
  }
  return maxNum;
}

Clever

function solution(digits){
  if (digits.length <= 5) return Number(digits);
  return Math.max(Number(digits.substr(0, 5)), solution(digits.substr(1)));
}

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对比

Clever Solution中使用了递归。

可是递归每次调用都会在内存中开辟新的空间，若数据过大，很容易引发堆栈溢出。