392. Is Subsequence

392.Is-Subsequence/benchmark_sols.py

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+import importlib.util
+import random
+import string
+import time
+from pathlib import Path
+
+DIR = Path(__file__).resolve().parent
+
+
+def load_module(name: str, path: Path):
+    spec = importlib.util.spec_from_file_location(name, path)
+    mod = importlib.util.module_from_spec(spec)
+    assert spec.loader is not None
+    spec.loader.exec_module(mod)
+    return mod
+
+
+def is_sub(sol, s: str, t: str) -> bool:
+    return sol.isSubsequence(s, t)
+
+
+def _ref_subsequence(s: str, t: str) -> bool:
+    if not s:
+        return True
+    i = 0
+    for c in t:
+        if c == s[i]:
+            i += 1
+            if i == len(s):
+                return True
+    return False
+
+
+def _random_string(n: int) -> str:
+    return "".join(random.choices(string.ascii_lowercase, k=n))
+
+
+def main() -> None:
+    mod1 = load_module("sol1_impl", DIR / "sol1.py")
+    mod3 = load_module("sol3_impl", DIR / "sol3.py")
+    sol1 = mod1.Solution()
+    sol3 = mod3.Solution()
+
+    random.seed(0)
+    cases: list[tuple[str, str]] = [
+        ("", "abc"),
+        ("abc", ""),
+        ("abc", "ahbgdc"),
+        ("axc", "ahbgdc"),
+        ("", ""),
+        ("a" * 100, "a" * 200 + "b" * 200),
+    ]
+    for _ in range(200):
+        la, lb = random.randint(0, 500), random.randint(0, 2000)
+        cases.append((_random_string(la), _random_string(lb)))
+
+    for s, t in cases:
+        is_sub(sol1, s, t)
+        is_sub(sol3, s, t)
+
+    reps = 50
+    t0 = time.perf_counter()
+    for _ in range(reps):
+        for s, t in cases:
+            is_sub(sol1, s, t)
+    t_sol1 = time.perf_counter() - t0
+
+    t0 = time.perf_counter()
+    for _ in range(reps):
+        for s, t in cases:
+            is_sub(sol3, s, t)
+    t_sol3 = time.perf_counter() - t0
+
+    print(f"sol1: {t_sol1 * 1000:.3f} ms")
+    print(f"sol3: {t_sol3 * 1000:.3f} ms")
+    ratio = t_sol3 / t_sol1
+    print(f"(sol3 / sol1: {ratio:.3f})")
+
+
+if __name__ == "__main__":
+    main()

392.Is-Subsequence/memo.md

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+# 392. Is Subsequence
+
+sとtに対してそれぞれindexを保存して最後まで一致させられるかどうかを判定する: sol1.py
+- 時間計算量 O(|t|)、空間計算量 O(1)
+
+書き終わって early return が可能なことに気が付く。index の取り方も変えた: sol2.py
+indexの取り方はもとのままの場合にも書く: sol3.py 添字の取り方が分かりやすいのでこちらの方が良さそう
+- 時間計算量 O(|t|)、空間計算量 O(1)
+- 漸近計算量では差がないが、early returnがある影響でこちらの方が早い
+
+https://discord.com/channels/1084280443945353267/1201211204547383386/1231637671831408821
+
+> これは、正規表現で s の文字のすべての間に .* を挟み込んで、マッチすればいいので、一回舐めれば解けそうですね
+
+> これは、本当はエスケープしないといけない
+
+正規表現を使ってかいてみる: sol4.py
+
+https://discord.com/channels/1084280443945353267/1225849404037009609/1243290893671465080
+
+関数型として書き、ループに直している
+再帰で書いてみる: sol5.py
+
+
+
+
+
+### 追記
+sol3.pyとsol1.pyの速度はそれほど変わらず、sol3.pyの方が遅い場合もあった
+
+sol1: 1532.053 ms
+sol3: 1710.168 ms
+(sol3 / sol1: 1.116)

392.Is-Subsequence/sol1.py

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+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        if not s:
+            return True
+        if not t:
+            return False
+
+        index_s = 0
+        index_t = 0
+        while index_t < len(t):
+            if s[index_s] == t[index_t]:
+                index_s += 1
+            if index_s == len(s):
+                return True
+            index_t += 1
+
+        return False

392.Is-Subsequence/sol1_revised.py

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+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        if not s:
+            return True
+        if not t:
+            return False
+
+        index_s = 0
+        for index_t in range(len(t)):
+            if s[index_s] == t[index_t]:
+                index_s += 1
+                if index_s == len(s):
+                    return True
+
+        return False

392.Is-Subsequence/sol2.py

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+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        if not s:
+            return True
+        if not t:
+            return False
+
+        remaining_num_s = len(s)
+        remaining_num_t = len(t)
+        while remaining_num_s <= remaining_num_t:
+            if s[len(s) - remaining_num_s] == t[len(t) - remaining_num_t]:
+                remaining_num_s -= 1
+            if remaining_num_s == 0:
+                return True
+            remaining_num_t -= 1
+
+        return False

392.Is-Subsequence/sol3.py

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+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        if not s:
+            return True
+        if not t:
+            return False
+
+        index_s = 0
+        index_t = 0
+        while len(s) - index_s <= len(t) - index_t:
+            if s[index_s] == t[index_t]:
+                index_s += 1
+            if index_s == len(s):
+                return True
+            index_t += 1
+
+        return False

392.Is-Subsequence/sol4.py

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+import re
+
+
+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        pattern = ""
+        for c in s:
+            pattern += ".*" + re.escape(c)
+        return re.match(pattern, t) is not None

392.Is-Subsequence/sol5.py

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+class Solution:
+    def isSubsequence(self, s: str, t: str) -> bool:
+        if len(s) == 0:
+            return True
+        if len(s) > len(t) or len(t) == 0:
+            return False
+        if s[0] == t[0]:
+            return self.isSubsequence(s[1:], t[1:])
+        return self.isSubsequence(s, t[1:])