Implement isomorphic-strings

name: isomorphic-strings
url: https://leetcode.com/problems/isomorphic-strings
difficulty: easy

time: 4ms
time-rank: 94.57%
time-complexity: O(N)

space: 7.1 MB
space-rank: 95.22%
space-complexity: O(1)

Fixes #290

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt

isomorphic-strings-test.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <gtest/gtest.h>
+
+#include "isomorphic-strings.cpp"
+
+using namespace std;
+
+TEST(IsomorphicStrings, egg_add) {
+  EXPECT_EQ(true, Solution().isIsomorphic("egg", "add"));
+}
+
+TEST(IsomorphicStrings, foo_bar) {
+  EXPECT_EQ(false, Solution().isIsomorphic("foo", "bar"));
+}
+
+TEST(IsomorphicStrings, paper_title) {
+  EXPECT_EQ(true, Solution().isIsomorphic("paper", "title"));
+}
+
+TEST(IsomorphicStrings, badc_bada) {
+  EXPECT_EQ(false, Solution().isIsomorphic("badc", "bada"));
+}

isomorphic-strings.cpp

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+// clang-format off
+// name: isomorphic-strings
+// url: https://leetcode.com/problems/isomorphic-strings
+// difficulty: 1
+// clang-format on
+
+#include <array>
+
+using namespace std;
+
+class Solution {
+public:
+  bool isIsomorphic(string s, string t) {
+    const size_t N = s.size();
+    const size_t M = t.size();
+
+    if (N != M) {
+      return false;
+    }
+
+    array<char, 128> lut;
+    lut.fill(-1);
+    array<char, 128> rlut;
+    rlut.fill(-1);
+
+    // i           0   1   2
+    // s[i]        e   g   g
+    // t[i]        a   d   d
+    // lut[s[i]]  -1  -1   d
+    // rlut[t[i]] -1  -1   g
+    //
+    // lut[]      e:a g:d
+    // rlut[]     a:e d:g
+
+    for (size_t i = 0; i < N; ++i) {
+      if (lut[s[i]] == char(-1)) {
+        if (rlut[t[i]] != char(-1)) {
+          return false;
+        }
+        lut[s[i]] = t[i];
+        rlut[t[i]] = s[i];
+        continue;
+      }
+
+      if (s[i] != rlut[t[i]]) {
+        return false;
+      }
+
+      if (t[i] != lut[s[i]]) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+};