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.
题意就是输入两个字符串,判断一个字符串是否可以由另外一个字符串删除一些字母得到。容易想到的一个贪心算法就是,只要遍历一遍t字符串,依次找出s字符串的每个字符。时间复杂度为o(n)。
class Solution {
public:
bool isSubsequence(string s, string t) {
int index = 0;
int s_pos = s[index];
for (int i = 0; i < t.length(); i++) {
if (t[i] == s_pos) {
index++;
s_pos = s[index];
}
}
if (index == s.length()) {
return true;
}
else {
return false;
}
}
};