CF223B.Two Strings

A subsequence of length |x| of string s = _s_1_s_2... s|s| (where |s| is the length of string s) is a string x = _s__k_1_s__k_2... s__k|x| (1 ≤ _k_1 < _k_2 < ... < k|x| ≤ |s|).

You've got two strings — s and t. Let's consider all subsequences of string s, coinciding with string t. Is it true that each character of string s occurs in at least one of these subsequences? In other words, is it true that for all i (1 ≤ i ≤ |s|), there is such subsequence x = _s__k_1_s__k_2... s__k|x| of string s, that x = t and for some j (1 ≤ j ≤ |x|) k__j = i.

字符串 $s = s_1 s_2 \dots s_{|s|}$（其中 $|s|$ 表示字符串 $s$ 的长度）的一个长度为 $|x|$ 的子序列是指形如 $x = s_{k_1} s_{k_2} \dots s_{k_{|x|}}$ 的字符串（满足 $1 \le k_1 < k_2 < \dots < k_{|x|} \le |s|$）。

给定两个字符串 $s$ 和 $t$。考虑字符串 $s$ 的所有与字符串 $t$ 相等的子序列。问：字符串 $s$ 的每个字符是否都至少出现在其中一个这样的子序列中？换言之，是否对每个 $i$（$1 \le i \le |s|$），均存在字符串 $s$ 的一个子序列 $x = s_{k_1} s_{k_2} \dots s_{k_{|x|}}$，使得 $x = t$，且对某个 $j$（$1 \le j \le |x|$）有 $k_j = i$？

The first line contains string s, the second line contains string t. Each line consists only of lowercase English letters. The given strings are non-empty, the length of each string does not exceed 2·105.

第一行包含字符串 $s$，第二行包含字符串 $t$。每行仅由小写英文字母组成。给定的字符串非空，且每个字符串的长度不超过 $2 \cdot 10^5$。

Print "Yes" (without the quotes), if each character of the string s occurs in at least one of the described subsequences, or "No" (without the quotes) otherwise.

如果字符串 $s$ 的每个字符都至少出现在一个所述子序列中，则输出 Yes（不带引号）；否则输出 No（不带引号）。

In the first sample string t can occur in the string s as a subsequence in three ways: abab, abab and abab. In these occurrences each character of string s occurs at least once.

In the second sample the 4-th character of the string s doesn't occur in any occurrence of string t.

In the third sample there is no occurrence of string t in string s.

在第一个样例中，字符串 $t$ 可以作为字符串 $s$ 的子序列以三种方式出现：abab、abab 和 abab。在这些出现中，字符串 $s$ 的每个字符至少出现一次。

在第二个样例中，字符串 $s$ 的第 4 个字符未出现在字符串 $t$ 的任何一次出现中。

在第三个样例中，字符串 $t$ 在字符串 $s$ 中没有任何出现。