[LeetCode392]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 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.

给定两个字符串s和t，判断s是否为t的子序列。只要s中的字符都在t中出现并且出现的先后顺序与s一致，那么s就是t的子序列。将s和t同时从左往右扫描，同时进行计数。如果当前位置字符相同，则s和t同时向右推移，计数值加1，否则t向右推移。一直到s和t中较短的那一个扫描完毕，如果计数值等于s的长度，那么s就是t的子序列，否则s不是t的子序列。算法的复杂度为O(n)。

class Solution {public:    bool isSubsequence(string s, string t) {        bool r;        int sn=s.length(),tn=t.length();        int count=0,i=0,j=0;        while(i<sn&&j<tn)        {            if(s[i]==t[j])            {                i++;                j++;                count++;            }            else            {                j++;            }        }        if(count==sn)        r=true;        else        r=false;        return r;    }};