is-subsequence.py

# V0 

# V1 
# https://blog.csdn.net/fuxuemingzhu/article/details/79568772
class Solution(object):
    def isSubsequence(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        queue = collections.deque(s)
        for c in t:
            if not queue: return True
            if c == queue[0]:
                queue.popleft()
        return not queue

# V1' 
# https://blog.csdn.net/fuxuemingzhu/article/details/79568772
class Solution(object):
    def isSubsequence(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        si, ti = 0, 0
        while si < len(s) and ti < len(t):
            if t[ti] == s[si]:
                si += 1
            ti += 1
        return si == len(s)

# V2 
# Time:  O(n)
# Space: O(1)
class Solution(object):
    def isSubsequence(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        if not s:
            return True

        i = 0
        for c in t:
            if c == s[i]:
                i += 1
            if i == len(s):
                break
        return i == len(s)