Is Subsequence

题目

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.

分析

    这是leetcode中一道中等难度题，归于Greedy（贪心）标签。本道题解题思路比较清晰，定义两个指针i、j，其中i用于字符串s，j用于字符串t，指针j每次循环都递增一次，当s[i] = s[j]时，指针i递增。最后如果i指向了s的末尾，则说明s是t的子串。

    算法复杂度为O(t.size())。

代码

class Solution {public:    bool isSubsequence(string s, string t) {        int m = s.size(), n = t.size();        int i,j;        for (i = 0, j = 0;i < m && j < n;j++)        if (s[i] == t[j])        i++;                return i == m;    }};