feat: solve day 7 part 1 and part 2

07/BridgeRepair/Equation.cs

@@ -0,0 +1,76 @@
+namespace BridgeRepair;
+
+// TODO: Look at what the public API should be here.
+class Equation(long testValue, List<long> numbers)
+{
+  public readonly long TestValue = testValue;
+
+  public bool IsPossible(bool isPart2 = false)
+  {
+    var configs = GeneratePossibleOperatorConfigurations(isPart2).ToList();
+    return configs.Select(Evaluate).Any(result => result == TestValue);
+  }
+
+  public long Evaluate(char[] operators)
+  {
+    var result = numbers[0];
+
+    for (var i = 0; i < operators.Length; i++)
+    {
+      var currentOperator = operators[i];
+      var number = numbers[i + 1];
+
+      if (currentOperator is '+')
+      {
+        result += number;
+        continue;
+      }
+
+      if (currentOperator is '*')
+      {
+        result *= number;
+        continue;
+      }
+
+      result = long.Parse(result + number.ToString());
+    }
+    
+    return result;
+  }
+  
+  public IEnumerable<char[]> GeneratePossibleOperatorConfigurations(bool isPart2 = false)
+  {
+    // TODO: make it possible to pass is operators we can use.
+    var numberOfPositions = numbers.Count - 1;
+    var config = new char[numberOfPositions];
+    var numOfOperators = isPart2 ? 3 : 2;
+    var numberOfPossibleConfigurations = Math.Pow(numOfOperators, numberOfPositions);
+
+    for (var i = 0; i < numberOfPossibleConfigurations; i++)
+    {
+      var j = 0;
+      
+      while (j < numberOfPositions)
+      {
+        var currentOperator = config[j];
+        
+        if (currentOperator is '+')
+        {
+          config[j] = '*';
+          break;
+        }
+
+        if (isPart2 && currentOperator is '*')
+        {
+          config[j] = '|';
+          break;
+        }
+
+        config[j] = '+';
+        j++;
+      }
+      
+      yield return config.ToArray();
+    }
+  }
+}