Restore IP Addresses

CMakeLists.txt

@@ -532,6 +532,7 @@ add_task(repeated-dna-sequences)
 add_task(repeated-string-match)
 add_task(repeated-substring-pattern)
 add_task(reshape-the-matrix)
+add_task(restore-ip-addresses)
 add_task(restore-the-array)
 add_task(reverse-bits)
 add_task(reverse-integer)

solutions/restore-ip-addresses/CMakeLists.txt

@@ -0,0 +1 @@
+add_catch(test_restore_ip_addresses test.cpp)

solutions/restore-ip-addresses/solution.hpp

@@ -0,0 +1,52 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+class Solution {
+public:
+  static std::vector<std::string> restoreIpAddresses(std::string s) {
+    std::vector<std::string> addresses;
+    std::vector<std::string> parts;
+    restoreIpAddresses(0, s, &parts, &addresses);
+    return addresses;
+  }
+
+private:
+  static void restoreIpAddresses(size_t i, const std::string &s,
+                                 std::vector<std::string> *parts,
+                                 std::vector<std::string> *addresses) {
+    if (i == s.size() && parts->size() == 4) {
+      addresses->push_back(buildIpAddress(*parts));
+      return;
+    }
+    if (i == s.size() || parts->size() == 4) {
+      return;
+    }
+    for (auto n : {1, 2, 3}) {
+      if (i + n > s.size()) {
+        return;
+      }
+      if (n > 1 && s[i] == '0') {
+        return;
+      }
+      if (255 < std::stoi(s.substr(i, n))) {
+        return;
+      }
+      parts->push_back(s.substr(i, n));
+      restoreIpAddresses(i + n, s, parts, addresses);
+      parts->pop_back();
+    }
+  }
+
+  static std::string buildIpAddress(const std::vector<std::string> &parts) {
+    std::string address;
+    for (size_t i = 0; i < 4; ++i) {
+      address += parts[i];
+      if (i != 3) {
+        address += '.';
+      }
+    }
+    return address;
+  }
+};

solutions/restore-ip-addresses/test.cpp

@@ -0,0 +1,31 @@
+#include <catch.hpp>
+
+#include <solution.hpp>
+
+TEST_CASE("Simple") {
+  struct TestCase {
+    std::string s;
+    std::vector<std::string> expected;
+  };
+
+  std::vector<TestCase> test_cases{
+      {
+          .s = "25525511135",
+          .expected{"255.255.11.135", "255.255.111.35"},
+      },
+      {
+          .s = "0000",
+          .expected{"0.0.0.0"},
+      },
+      {
+          .s = "101023",
+          .expected{"1.0.10.23", "1.0.102.3", "10.1.0.23", "10.10.2.3",
+                    "101.0.2.3"},
+      },
+  };
+
+  for (const auto &[s, expected] : test_cases) {
+    const auto actual = Solution::restoreIpAddresses(s);
+    REQUIRE(expected == actual);
+  }
+}