upd

algorithms/labs/lab8/code/comp/2.py

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+def longest_common_len_naive(strs, k):
+    s0 = strs[0]
+    best = 0
+    for i in range(len(s0)):
+        for j in range(i + 1, len(s0) + 1):
+            sub = s0[i:j]
+            cnt = 0
+            for s in strs:
+                if sub in s:
+                    cnt += 1
+            if cnt >= k and j - i > best:
+                best = j - i
+    return best
+
+
+def longest_common_len_optimized(strs, k):
+    import sys
+
+    def has_len(L):
+        if L == 0:
+            return True
+        base = 911382323
+        mod = 10**9 + 7
+        powL = pow(base, L - 1, mod)
+        commons = None
+        for s in strs:
+            if L > len(s):
+                return False
+            h = 0
+            st = set()
+            for t in range(L):
+                h = (h * base + ord(s[t])) % mod
+            st.add(h)
+            for t in range(L, len(s)):
+                h = (h - ord(s[t - L]) * powL) % mod
+                h = (h * base + ord(s[t])) % mod
+                st.add(h)
+            if commons is None:
+                commons = st
+            else:
+                commons &= st
+            if not commons:
+                return False
+        return len(commons) >= k
+
+    lo, hi = 0, min(len(s) for s in strs)
+    ans = 0
+    while lo <= hi:
+        mid = (lo + hi) // 2
+        if has_len(mid):
+            ans = mid
+            lo = mid + 1
+        else:
+            hi = mid - 1
+    return ans
+
+
+if __name__ == "__main__":
+    strs = ["abracadabra", "cadabracad", "dabrac"]
+    print(longest_common_len_naive(strs, 2))
+    print(longest_common_len_optimized(strs, 2))