Friday, May 17, 2013

Find Next Higher Number With Same Digits

Write a program to find the next highest number by rearranging the digits of a number. For instance,
If input is 13483 then output must be 13834.

Test cases:
Input     Output
3971     7139
83971   87139
54321   54321
405321 410235

Logic:
Let take a numner 12543 and resulting next higher number is 13245.
Scan the digits from the tenths digit going towards left (which is 4 in our case)
At each iteration we check the right digit of the current digit we are at and if the value of the right is greater then current we stop other continue to left
4>3 continue
5>4 contine
2>5 stop
2 is our pivot element.
from the digit 2 to the right we find the smallest higher digit of resulting number 2 which 3.
swap the 3 with 2, it will become 13542. now 3 is our pivot element.
Now revere the number to right pivot element i.e 3 , it comes 13245 result.
Note : in case of repeating digit like 147553 we need to swap the 4 with the rightmost digit, otherwise we don't get the highest number.
Time complexity would be O(n)

Code

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