我刚刚搞砸了一次面试,而且我的面试问题几乎毫无进展。

给定一个数,找出下一个与之完全相同的更大的数 作为原始数字的数字集。例如:给定38276返回 38627

我想从找到第一个比个位小的数字的下标开始。然后我将旋转子集中的最后一个数字,这样它是由相同的数字组成的下一个最大的数字,但卡住了。

面试官还建议我试着一次换一个数字,但我搞不懂算法,只能盯着屏幕看20-30分钟。不用说,我想我还得继续找工作。


当前回答

如果你用c++编程,你可以使用next_permutation:

#include <algorithm>
#include <string>
#include <iostream>

int main(int argc, char **argv) {
  using namespace std; 
   string x;
   while (cin >> x) {
    cout << x << " -> ";
    next_permutation(x.begin(),x.end());
    cout << x << "\n";
  }
  return 0;
}

其他回答

一个几乎相同的问题出现了Code Jam问题,这里有一个解决方案:

http://code.google.com/codejam/contest/dashboard?c=186264#s=a&a=1

下面用一个例子总结一下这个方法:

34722641

A.将数字序列分成两部分,使右边的部分尽可能长,同时保持递减顺序:

34722 641

(如果整个数字是递减的,就没有比这个数字更大的数字了。)

在这一点上,你知道没有从左边开始的更大的数了,因为右边的剩余数字已经尽可能大了。

责任。选择第一个序列的最后一位:

3472(2) 641

B.2。找出第二个序列中比它大的最小的数字:

3472(2) 6(4)1

你要做的就是找到左边可能的最小增量。

B.3。交换:

3472(2) 6(4)1
->
3472(4) 6(2)1
->
34724 621

C.将第二个序列按递增顺序排序:

34724 126

d .完成了!

34724126

你把这个数字分开,这样你就知道没有更大的数字具有相同的左边部分,你把左边部分增加了尽可能小的量,你让剩下的右边部分尽可能小,所以你可以确保这个新数字是用相同的数字集合可以得到的最小的更大的数字。

这是个很有趣的问题。

这是我的java版本。在我检查其他贡献者的评论之前,从弄清楚模式到完全完成代码,我花了大约3个小时。很高兴看到我的想法和别人一样。

O (n)的解决方案。老实说,如果时间只有15分钟,并且要求在白板上完成完整的代码,我将会失败。

以下是我的解决方案的一些有趣点:

避免任何排序。 完全避免字符串操作 实现O(logN)空间复杂度

我在代码中添加了详细注释,并在每个步骤中添加了大O。

  public int findNextBiggestNumber(int input  )   {
    //take 1358642 as input for example.
    //Step 1: split the whole number to a list for individual digital   1358642->[2,4,6,8,5,3,1]
    // this step is O(n)
    int digitalLevel=input;

    List<Integer> orgNumbersList=new ArrayList<Integer>()   ;

    do {
        Integer nInt = new Integer(digitalLevel % 10);
        orgNumbersList.add(nInt);

        digitalLevel=(int) (digitalLevel/10  )  ;


    } while( digitalLevel >0)    ;
    int len= orgNumbersList.size();
    int [] orgNumbers=new int[len]  ;
    for(int i=0;i<len;i++){
        orgNumbers[i ]  =  orgNumbersList.get(i).intValue();
    }
    //step 2 find the first digital less than the digital right to it
    // this step is O(n)


    int firstLessPointer=1;
    while(firstLessPointer<len&&(orgNumbers[firstLessPointer]>orgNumbers[ firstLessPointer-1 ])){
        firstLessPointer++;
    }
     if(firstLessPointer==len-1&&orgNumbers[len-1]>=orgNumbers[len-2]){
         //all number is in sorted order like 4321, no answer for it, return original
         return input;
     }

    //when step 2 step finished, firstLessPointer  pointing to number 5

     //step 3 fristLessPointer found, need to find  to  first number less than it  from low digital in the number
    //This step is O(n)
    int justBiggerPointer=  0 ;

    while(justBiggerPointer<firstLessPointer&& orgNumbers[justBiggerPointer]<orgNumbers[firstLessPointer]){
        justBiggerPointer++;
    }
    //when step 3 finished, justBiggerPointer  pointing to 6

    //step 4 swap the elements  of justBiggerPointer and firstLessPointer .
    // This  is O(1) operation   for swap

   int tmp=  orgNumbers[firstLessPointer] ;

    orgNumbers[firstLessPointer]=  orgNumbers[justBiggerPointer]  ;
     orgNumbers[justBiggerPointer]=tmp ;


     // when step 4 finished, the list looks like        [2,4,5,8,6,3,1]    the digital in the list before
     // firstLessPointer is already sorted in our previous operation
     // we can return result from this list  but  in a differrent way
    int result=0;
    int i=0;
    int lowPointer=firstLessPointer;
    //the following pick number from list from  the position just before firstLessPointer, here is 8 -> 5 -> 4 -> 2
    //This Operation is O(n)
    while(lowPointer>0)        {
        result+= orgNumbers[--lowPointer]* Math.pow(10,i);
        i++;
    }
    //the following pick number from list   from position firstLessPointer
    //This Operation is O(n)
    while(firstLessPointer<len)        {
        result+= orgNumbers[firstLessPointer++ ]* Math.pow(10,i);
        i++;
    }
     return  result;

}

下面是在Intellj中运行的结果:

959879532-->959892357
1358642-->1362458
1234567-->1234576
77654321-->77654321
38276-->38627
47-->74

非常简单的实现使用Javascript,下一个最高的数字与相同的数字

/*
Algorithm applied
I) Traverse the given number from rightmost digit, keep traversing till you find a digit which is smaller than the previously traversed digit. For example, if the input number is “534976”, we stop at 4 because 4 is smaller than next digit 9. If we do not find such a digit, then output is “Not Possible”.

II) Now search the right side of above found digit ‘d’ for the smallest digit greater than ‘d’. For “534976″, the right side of 4 contains “976”. The smallest digit greater than 4 is 6.

III) Swap the above found two digits, we get 536974 in above example.

IV) Now sort all digits from position next to ‘d’ to the end of number. The number that we get after sorting is the output. For above example, we sort digits in bold 536974. We get “536479” which is the next greater number for input 534976.

*/

function findNext(arr)
{
  let i;
  //breaking down a digit into arrays of string and then converting back that array to number array
  let arr1=arr.toString().split('').map(Number) ;
  //started to loop from the end of array 
  for(i=arr1.length;i>0;i--)
  {
    //looking for if the current number is greater than the number next to it
    if(arr1[i]>arr1[i-1])
    {// if yes then we break the loop it so that we can swap and sort
      break;}
  }

  if(i==0)
  {console.log("Not possible");}

   else
  {
   //saving that big number and smaller number to the left of it
   let smlNum =arr1[i-1];
    let bigNum =i;
   /*now looping again and checking if we have any other greater number, if we have one AFTER big number and smaller number to the right. 
     A greater number that is of course greater than that smaller number but smaller than the first number we found.
     Why are doing this? Because that is an algorithm to find next higher number with same digits. 
   */
    for(let j=i+1;j<arr1.length;j++)
      {//What if there are no digits afters those found numbers then of course loop will not be initiated otherwise...
        if(arr1[j]> smlNum && arr1[j]<arr1[i])
        {// we assign that other found number here and replace it with the one we found before
          bigNum=j;

        }
      } //now we are doing swapping of places the small num and big number , 3rd part of alogorithm
    arr1[i-1]=arr1[bigNum];
          arr1[bigNum]=smlNum;
    //returning array 
    //too many functions applied sounds complicated right but no, here is the  trick
    //return arr first then apply each function one by one to see output and then further another func to that output to match your needs
    // so here after swapping , 4th part of alogorithm is to sort the array right after the 1st small num we found
    // to do that first we simple take part of array, we splice it and then we apply sort fucntion, then check output (to check outputs, pls use chrome dev console)
    //and then  simply the rest concat and join to main one digit again.
     return arr1.concat((arr1.splice(i,arr1.length)).sort(function(a, b){return a-b})).join('');



    // Sorry to make it too long but its fun explaining things in much easier ways as much as possible!!
  }

}


findNext(1234);

因为有很多评论,所以你最好把它复制到你的文本编辑器。 谢谢!

这是我在Ruby中的实现:

def foo num  
  num = num.to_s.chars.map(&:to_i)
  return num.join.to_i if num.size < 2
  for left in (num.size-2).downto(0) do
    for right in (num.size-1).downto(left+1) do
      if num[right]>num[left]
        num[left],num[right] = num[right],num[left]        
        return (num[0..left] + num[left+1..num.size-1].sort).join.to_i
      end
    end
  end
  return num.join.to_i
end

p foo 38276 
#will print: 38627

下面是生成一个数字的所有排列的代码..不过必须先使用string . valueof (integer)将该整数转换为字符串。

/**
 * 
 * Inserts a integer at any index around string.
 * 
 * @param number
 * @param position
 * @param item
 * @return
 */
public String insertToNumberStringAtPosition(String number, int position,
        int item) {
    String temp = null;
    if (position >= number.length()) {
        temp = number + item;
    } else {
        temp = number.substring(0, position) + item
                + number.substring(position, number.length());
    }
    return temp;
}

/**
 * To generate permutations of a number.
 * 
 * @param number
 * @return
 */
public List<String> permuteNumber(String number) {
    List<String> permutations = new ArrayList<String>();
    if (number.length() == 1) {
        permutations.add(number);
        return permutations;
    }
    // else
    int inserterDig = (int) (number.charAt(0) - '0');
    Iterator<String> iterator = permuteNumber(number.substring(1))
            .iterator();
    while (iterator.hasNext()) {
        String subPerm = iterator.next();
        for (int dig = 0; dig <= subPerm.length(); dig++) {
            permutations.add(insertToNumberStringAtPosition(subPerm, dig,
                    inserterDig));
        }
    }
    return permutations;
}