leetCode--- Is Subsequence

一. 题目：Is Subsequence

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 sis 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.

二. 思路分析

          题目大意：判断s是否为t的子序列。s = "abc", t = "ahbgdc"，返回true；s=’’abcde’’, t=”aec”，返回false。思路分析：我们可以用两个指针分别指向字符串s和t，然后如果字符相等，则i和j自增1，反之只有j自增1，最后看i是否等于s的长度，等于说明s已经遍历完了，而且字符都有在t中出现过，参见代码如下：

bool isSubsequence(string s, string t) {        int i, j;        for (i = 0, j = 0; i < t.length(); i++) {            if (j == s.length())                break;            if (t[i] == s[j])                j++;        }        return j == s.length();    }