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

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;
}

我只测试了两个数字。他们工作。 在去年12月退休之前,我做了8年的IT经理,我关心三件事: 1)准确性:如果它总是有效,那就很好。 2)速度:用户可以接受。 3)明确:我可能没有你聪明,但我付你薪水。确保你用英语解释你在做什么。

奥马尔,祝你好运。

Sub Main()

Dim Base(0 To 9) As Long
Dim Test(0 To 9) As Long

Dim i As Long
Dim j As Long
Dim k As Long
Dim ctr As Long

Const x As Long = 776914648
Dim y As Long
Dim z As Long

Dim flag As Boolean

' Store the digit count for the original number in the Base vector.
    For i = 0 To 9
        ctr = 0
        For j = 1 To Len(CStr(x))
            If Mid$(CStr(x), j, 1) = i Then ctr = ctr + 1
        Next j
        Base(i) = ctr
    Next i

' Start comparing from the next highest number.
    y = x + 1
    Do

' Store the digit count for the each new number in the Test vector.
        flag = False
        For i = 0 To 9
            ctr = 0
            For j = 1 To Len(CStr(y))
                If Mid$(CStr(y), j, 1) = i Then ctr = ctr + 1
            Next j
            Test(i) = ctr
        Next i

' Compare the digit counts.
        For k = 0 To 9
            If Test(k) <> Base(k) Then flag = True
        Next k

' If no match, INC and repeat.
        If flag = True Then
            y = y + 1
            Erase Test()
        Else
            z = y ' Match.
        End If

    Loop Until z > 0

    MsgBox (z), , "Solution"

End Sub

这是另一个Java实现,可以开箱即用,并通过测试完成。 这个解决方案是O(n)个空间和时间,使用老式的动态规划。

如果你想用蛮力,有两种蛮力:

排列所有的东西,然后选择最小值更高的:O(n!) 与此实现类似,但不是DP,而是强制填充的步骤 indexToIndexOfNextSmallerLeft映射将在O(n²)中运行。


import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class NextHigherSameDigits {

    public long next(final long num) {
        final char[] chars = String.valueOf(num).toCharArray();
        final int[] digits = new int[chars.length];
        for (int i = 0; i < chars.length; i++) {
            digits[i] = Character.getNumericValue(chars[i]);
        }

        final Map<Integer, Integer> indexToIndexOfNextSmallerLeft = new HashMap<>();
        indexToIndexOfNextSmallerLeft.put(1, digits[1] > digits[0] ? 0 : null);
        for (int i = 2; i < digits.length; i++) {
            final int left = digits[i - 1];
            final int current = digits[i];
            Integer indexOfNextSmallerLeft = null;
            if (current > left) {
                indexOfNextSmallerLeft = i - 1;
            } else {
                final Integer indexOfnextSmallerLeftOfLeft = indexToIndexOfNextSmallerLeft.get(i - 1);
                final Integer nextSmallerLeftOfLeft = indexOfnextSmallerLeftOfLeft == null ? null : 
                    digits[indexOfnextSmallerLeftOfLeft];

                if (nextSmallerLeftOfLeft != null && current > nextSmallerLeftOfLeft) {
                    indexOfNextSmallerLeft = indexOfnextSmallerLeftOfLeft;
                } else {
                    indexOfNextSmallerLeft = null;
                }
            }

            indexToIndexOfNextSmallerLeft.put(i, indexOfNextSmallerLeft);
        }

        Integer maxOfindexOfNextSmallerLeft = null;
        Integer indexOfMinToSwapWithNextSmallerLeft = null;
        for (int i = digits.length - 1; i >= 1; i--) {
            final Integer indexOfNextSmallerLeft = indexToIndexOfNextSmallerLeft.get(i);
            if (maxOfindexOfNextSmallerLeft == null ||
                    (indexOfNextSmallerLeft != null && indexOfNextSmallerLeft > maxOfindexOfNextSmallerLeft)) {

                maxOfindexOfNextSmallerLeft = indexOfNextSmallerLeft;
                if (maxOfindexOfNextSmallerLeft != null && (indexOfMinToSwapWithNextSmallerLeft == null || 
                        digits[i] < digits[indexOfMinToSwapWithNextSmallerLeft])) {

                    indexOfMinToSwapWithNextSmallerLeft = i;
                }
            }
        }

        if (maxOfindexOfNextSmallerLeft == null) {
            return -1;
        } else {
            swap(digits, indexOfMinToSwapWithNextSmallerLeft, maxOfindexOfNextSmallerLeft);
            reverseRemainingOfArray(digits, maxOfindexOfNextSmallerLeft + 1);
            return backToLong(digits);
        }
    }

    private void reverseRemainingOfArray(final int[] digits, final int startIndex) {
        final int[] tail = Arrays.copyOfRange(digits, startIndex, digits.length);
        for (int i = tail.length - 1; i >= 0; i--) {
            digits[(digits.length - 1)  - i] = tail[i];                 
        }
    }

    private void swap(final int[] digits, final int currentIndex, final int indexOfNextSmallerLeft) {
        int temp = digits[currentIndex];
        digits[currentIndex] = digits[indexOfNextSmallerLeft];
        digits[indexOfNextSmallerLeft] = temp;
    }

    private long backToLong(int[] digits) {     
        StringBuilder sb = new StringBuilder();
        for (long i : digits) {
            sb.append(String.valueOf(i));
        }

        return Long.parseLong(sb.toString());
    }

    @Test
    public void test() {
        final long input1 =    34722641;
        final long expected1 = 34724126;
        final long output1 = new NextHigherSameDigits().next(input1);
        assertEquals(expected1, output1);

        final long input2 =    38276;
        final long expected2 = 38627;
        final long output2 = new NextHigherSameDigits().next(input2);
        assertEquals(expected2, output2);

        final long input3 =    54321;
        final long expected3 = -1;
        final long output3 = new NextHigherSameDigits().next(input3);
        assertEquals(expected3, output3);

        final long input4 =    123456784987654321L;
        final long expected4 = 123456785123446789L;
        final long output4 = new NextHigherSameDigits().next(input4);
        assertEquals(expected4, output4);

        final long input5 =    9999;
        final long expected5 = -1;
        final long output5 = new NextHigherSameDigits().next(input5);
        assertEquals(expected5, output5);
    }

}

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!

function foo(num){
 sortOld = num.toString().split("").sort().join('');
 do{
    num++;
   sortNew = num.toString().split("").sort().join('');
 }while(sortNew!==sortOld);
 return num;
}