【LeetCode】392. Is Subsequence
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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
.
题解:
题目很容易想到的思路是,两层循环,在t中找s的每一个字符是否存在,但由于t有可能为一个十分长的string,按这种暴力做法,当t很长的时候,就会错误。就像错解那样。
正确答案采取的方法很巧妙,只有一层循环,s和t相同元素时,就把s的下标增加1,最后返回值是看s的下标是否与s的长度相等。
错解:
bool isSubsequence(string s, string t)
{
int k=0;
for(int i=0;i<s.size();i++)
{
for(;k<t.size();k++)
{
if(s[i]==t[k]&&i==s.size()-1)
return 1;
else if(s[i]==t[k]&&k!=t.size()-1)
break;
else if(s[i]!=t[k]&&k==t.size()-1)
return 0;
}
}
}
答案:
bool isSubsequence(string s, string t) {
int s_len = s.size(), s_index = 0, t_len = t.size();
for (int i=0; i<t_len && s_index<s_len; i++)
if (t[i]==s[s_index]) s_index++;
return s_index==s_len;
}
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