670. maximum swap

You are given an integer num. You can swap two digits at most once to get the maximum valued number.

Return the maximum valued number you can get.

solution

Construct a map that stores the right most index of each digit!

def maximumSwap(self, num: int) -> int:
	"""
	fully descending - no larger number
 
	first digit from right that has larger digit to the right
	should be swapped with the rightmost instance of the largest
	of those digits.
	"""
	sn = list(str(num))
	last_seen = [-1]*10
	  
	for i, digit in enumerate(sn):
		last_seen[int(digit)] = i
	  
	# iterate from left of num
	for i, digit in enumerate(sn):
		# check for digits larger than the digit
		# from 9 -> digit+1
		for j in reversed(range(int(digit)+1, 10)):
			if last_seen[j] > -1 and last_seen[j] > i:
				sn[i], sn[last_seen[j]] = sn[last_seen[j]], sn[i]
				return int("".join(sn))
	return num