isSubstring.py

# Given a string s and a string t, check if s is subsequence of t.
#
# You may assume that there is only lower case English letters in both s and t.
# t is potentially a very long (length ~= 500,000) string, and s is a short
# string (<=100).
#
# A subsequence of a string is a new string which is formed from the original
# string by deleting some (can be none) of the characters without disturbing
# the relative positions of the remaining characters. (ie, "ace" is a
# subsequence of "abcde" while "aec" is not).
#
# Example 1:
# s = "abc", t = "ahbgdc"
#
# Return true.
#
# Example 2:
# s = "axc", t = "ahbgdc"
#
# Return false.


class Solution(object):
    def isSubsequence(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        i = len(s) - 1
        j = len(t) - 1
        while(i >= 0 and j >= 0):
            if s[i] == t[j]:
                i -= 1
            j -= 1
        return i < 0