maximum-swap.py

# Time:  O(logn), logn is the length of the number string
# Space: O(logn)

# Given a non-negative integer, you could swap two digits at most once
# to get the maximum valued number. Return the maximum valued number you could get.
#
# Example 1:
# Input: 2736
# Output: 7236
# Explanation: Swap the number 2 and the number 7.
# Example 2:
# Input: 9973
# Output: 9973
# Explanation: No swap.
# Note:
# The given number is in the range [0, 10^8]

class Solution(object):
    def maximumSwap(self, num):
        """
        :type num: int
        :rtype: int
        """
        digits = list(str(num))
        left, right = 0, 0
        max_idx = len(digits)-1
        for i in reversed(xrange(len(digits))):
            if digits[i] > digits[max_idx]:
                max_idx = i
            elif digits[max_idx] > digits[i]:
                left, right = i, max_idx
        digits[left], digits[right] = digits[right], digits[left]
        return int("".join(digits))