Day 4

.vscode/settings.json

@@ -39,6 +39,7 @@
         "xstddef": "cpp",
         "xstring": "cpp",
         "xtr1common": "cpp",
-        "xutility": "cpp"
+        "xutility": "cpp",
+        "algorithm": "cpp"
     }
 }

2019/4thDay/challenge.txt

@@ -0,0 +1,25 @@
+--- Day 4: Secure Container ---
+You arrive at the Venus fuel depot only to discover it's protected by a password. The Elves had written the password on a sticky note, but someone threw it out.
+
+However, they do remember a few key facts about the password:
+
+It is a six-digit number.
+The value is within the range given in your puzzle input.
+Two adjacent digits are the same (like 22 in 122345).
+Going from left to right, the digits never decrease; they only ever increase or stay the same (like 111123 or 135679).
+Other than the range rule, the following are true:
+
+111111 meets these criteria (double 11, never decreases).
+223450 does not meet these criteria (decreasing pair of digits 50).
+123789 does not meet these criteria (no double).
+How many different passwords within the range given in your puzzle input meet these criteria?
+
+--- Part Two ---
+An Elf just remembered one more important detail: the two adjacent matching digits are not part of a larger group of matching digits.
+
+Given this additional criterion, but still ignoring the range rule, the following are now true:
+
+112233 meets these criteria because the digits never decrease and all repeated digits are exactly two digits long.
+123444 no longer meets the criteria (the repeated 44 is part of a larger group of 444).
+111122 meets the criteria (even though 1 is repeated more than twice, it still contains a double 22).
+How many different passwords within the range given in your puzzle input meet all of the criteria?

2019/4thDay/challenge1.cpp

@@ -0,0 +1,45 @@
+#include <iostream>
+#include <string>
+
+bool checkPassword( std::string pass )
+{
+
+    // Is less than 6
+    if ( pass.length() > 6 || pass.length() < 6 ) return false;
+
+    // Have any repeats
+    bool repeats = false;
+    char lastr = pass[0];
+    for ( int i = 1; i < pass.length(); i++ )
+    {
+        if ( lastr == pass[i] ) repeats = true;
+        lastr = pass[i];
+    }
+
+    if ( !repeats ) return false;
+
+    // Digets never decrease
+    bool decreases = true;
+    for ( int i = 1; i < pass.length(); i++ )
+        if ( pass[i - 1] > pass[i] ) decreases = false;
+
+    if ( !decreases ) return false;
+
+    return true;
+
+}
+
+int main(int argc, char** argv)
+{
+    
+    int upper = 893698;
+    int lower = 367479;
+
+    int accumilator = 0;
+    for ( int i = lower; i < upper; i++ )
+        if ( checkPassword( std::to_string( i ) ) )
+            accumilator++;
+
+    std::cout << "There are : " << accumilator << " valid passwords" << std::endl;
+
+}

2019/4thDay/challenge2.cpp

@@ -0,0 +1,44 @@
+#include <algorithm>
+#include <iostream>
+#include <string>
+
+bool checkPassword( std::string pass )
+{
+
+    // Is less than 6
+    if ( pass.length() > 6 || pass.length() < 6 ) return false;
+
+    // Digets never decrease
+    bool decreases = true;
+    for ( int i = 1; i < pass.length(); i++ )
+        if ( pass[i - 1] > pass[i] ) decreases = false;
+
+    if ( !decreases ) return false;
+
+    // No repeats ( conform w part 2 rule )
+    if ( std::any_of( pass.begin(), pass.end(), 
+    [&]( auto d ) {
+        return std::count( pass.begin(), pass.end(), d ) == 2; 
+    } ) )
+    {
+        return true;
+    }
+
+    return false;
+
+}
+
+int main(int argc, char** argv)
+{
+
+    int upper = 893698;
+    int lower = 367479;
+
+    int accumilator = 0;
+    for ( int i = lower; i < upper; i++ )
+        if ( checkPassword( std::to_string( i ) ) )
+            accumilator++;
+
+    std::cout << "There are : " << accumilator << " valid passwords" << std::endl;
+
+}