Is one string a subsequence of another

def is_subsequence(s, t):
    i = 0
    for c in t:                          # j walks t; i only moves on a match
        if i < len(s) and s[i] == c:
            i += 1
    return i == len(s)

#include <string>

bool solve(const std::string& s, const std::string& t) {
    size_t i = 0;
    for (size_t j = 0; j < t.size() && i < s.size(); ++j)   // j walks t; i only moves on a match
        if (s[i] == t[j]) ++i;
    return i == s.size();
}

class Solution {
    public boolean isSubsequence(String s, String t) {
        int i = 0;
        for (int j = 0; j < t.length() && i < s.length(); j++)   // j walks t; i only moves on a match
            if (s.charAt(i) == t.charAt(j)) i++;
        return i == s.length();
    }
}

function isSubsequence(s, t) {
  let i = 0;
  for (let j = 0; j < t.length && i < s.length; j++)   // j walks t; i only moves on a match
    if (s[i] === t[j]) i++;
  return i === s.length;
}

fn solve(s: &str, t: &str) -> bool {
    let s = s.as_bytes();
    let mut i = 0;
    for &c in t.as_bytes() {             // j walks t; i only moves on a match
        if i < s.len() && s[i] == c { i += 1; }
    }
    i == s.len()
}

solve :: String -> String -> Bool
solve [] _ = True
solve _ [] = False
solve (x : xs) (y : ys)
  | x == y    = solve xs ys          -- match it here, at the earliest place
  | otherwise = solve (x : xs) ys    -- skip this letter of t