Added older advents

advent_of_code_2015/day5/main2.cc

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+#include <algorithm>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+bool has_repeating_pair(string const &text)
+{
+    for (size_t idx = 0; idx < text.size() - 2; ++idx)
+    {
+        if (text.find(text.substr(idx, 2), idx + 2) != string::npos)
+        {
+            cout << "'" << text << "' has repeating pair: '";
+            cout << text.substr(idx, 2) << "'\n";
+            return true;
+        }
+    }
+
+    // cout << "'" << text << "' has no repeating pair\n";
+    return false;
+}
+
+bool repeats_plus_one(string const &text)
+{
+    for (size_t idx = 0; idx < text.size() - 2; ++idx)
+    {
+        if (text[idx] == text[idx + 2])
+            return true;
+    }
+
+    return false;
+}
+
+int main()
+{
+    string buffer;
+    size_t count = 0;
+
+    while (getline(cin, buffer))
+    {
+        if (has_repeating_pair(buffer)
+            && repeats_plus_one(buffer))
+        {
+            ++count;
+        }
+    }
+
+    cout << "Nice strings: " << count << "\n";
+
+}