Leetcode 392 Is Subsequence

Leetcode 392 Is Subsequence

Description

iven 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. 

题解

这道题比较简单，找出字符串s是否是t的字串，用bool数组ans从头到尾遍历，ans[i]为true的条件是s[i] == t[i]情况下i == 0或者ans[i - 1] == true，最后输出最后一位的值，代码如下:

class Solution {
public:
    bool isSubsequence(string s, string t) {
        if (s.size() <= 0)
            return true;
        vector<bool> ans(s.size(), false);
        int j = 0;
        for (int i = 0; i < t.size(); i++) {
            if (s[j] == t[i] && (s[j] || j == 0)) {
                ans[j++] = true;
            }
        }
        return ans[s.size() - 1];
    }
};