5.linq

<Query Kind="Program" />

void Main()
{
    int p1 = Compute(1);
    int p2 = Compute(5);
    
    $"P1: {p1}".Dump();
    $"P2: {p2}".Dump();
}

const int ImmediateMode = 1;

int Compute(int input)
{
    string inputString = "3,225,1,225,6,6,1100,1,238,225,104,0,101,71,150,224,101,-123,224,224,4,224,102,8,223,223,101,2,224,224,1,224,223,223,2,205,209,224,1001,224,-3403,224,4,224,1002,223,8,223,101,1,224,224,1,223,224,223,1101,55,24,224,1001,224,-79,224,4,224,1002,223,8,223,101,1,224,224,1,223,224,223,1,153,218,224,1001,224,-109,224,4,224,1002,223,8,223,101,5,224,224,1,224,223,223,1002,201,72,224,1001,224,-2088,224,4,224,102,8,223,223,101,3,224,224,1,223,224,223,1102,70,29,225,102,5,214,224,101,-250,224,224,4,224,1002,223,8,223,1001,224,3,224,1,223,224,223,1101,12,52,225,1101,60,71,225,1001,123,41,224,1001,224,-111,224,4,224,102,8,223,223,1001,224,2,224,1,223,224,223,1102,78,66,224,1001,224,-5148,224,4,224,1002,223,8,223,1001,224,2,224,1,223,224,223,1101,29,77,225,1102,41,67,225,1102,83,32,225,1101,93,50,225,1102,53,49,225,4,223,99,0,0,0,677,0,0,0,0,0,0,0,0,0,0,0,1105,0,99999,1105,227,247,1105,1,99999,1005,227,99999,1005,0,256,1105,1,99999,1106,227,99999,1106,0,265,1105,1,99999,1006,0,99999,1006,227,274,1105,1,99999,1105,1,280,1105,1,99999,1,225,225,225,1101,294,0,0,105,1,0,1105,1,99999,1106,0,300,1105,1,99999,1,225,225,225,1101,314,0,0,106,0,0,1105,1,99999,1107,677,677,224,1002,223,2,223,1005,224,329,101,1,223,223,7,677,677,224,1002,223,2,223,1005,224,344,1001,223,1,223,7,226,677,224,102,2,223,223,1006,224,359,101,1,223,223,1108,226,226,224,1002,223,2,223,1005,224,374,1001,223,1,223,8,226,677,224,1002,223,2,223,1006,224,389,1001,223,1,223,1108,226,677,224,1002,223,2,223,1006,224,404,101,1,223,223,1107,677,226,224,102,2,223,223,1006,224,419,101,1,223,223,1007,677,677,224,1002,223,2,223,1005,224,434,101,1,223,223,7,677,226,224,102,2,223,223,1006,224,449,1001,223,1,223,1008,226,677,224,1002,223,2,223,1006,224,464,101,1,223,223,8,677,677,224,1002,223,2,223,1006,224,479,101,1,223,223,108,226,226,224,102,2,223,223,1005,224,494,101,1,223,223,1107,226,677,224,1002,223,2,223,1006,224,509,101,1,223,223,107,226,226,224,1002,223,2,223,1006,224,524,1001,223,1,223,107,677,677,224,1002,223,2,223,1005,224,539,101,1,223,223,1007,226,226,224,102,2,223,223,1006,224,554,101,1,223,223,108,677,677,224,102,2,223,223,1005,224,569,101,1,223,223,107,677,226,224,102,2,223,223,1005,224,584,101,1,223,223,1008,226,226,224,102,2,223,223,1006,224,599,101,1,223,223,1108,677,226,224,1002,223,2,223,1006,224,614,101,1,223,223,8,677,226,224,102,2,223,223,1005,224,629,1001,223,1,223,1008,677,677,224,102,2,223,223,1006,224,644,101,1,223,223,1007,226,677,224,102,2,223,223,1005,224,659,101,1,223,223,108,226,677,224,102,2,223,223,1006,224,674,101,1,223,223,4,223,99,226";
    int[] memory = inputString.Split(',').Select(i => int.Parse(i)).ToArray();
    
    int ip = 0;
    int output = int.MinValue;
    
    while (ip >= 0 && ip < memory.Length)
    {
        string instruction = memory[ip].ToString();
        int opcode = instruction.Length >= 2 ? int.Parse(instruction.Substring(instruction.Length - 2)): int.Parse(instruction);
        int aMode = instruction.Length >= 3 ? int.Parse(instruction.Substring(instruction.Length - 3, 1)) : 0;
        int bMode = instruction.Length >= 4 ? int.Parse(instruction.Substring(instruction.Length - 4, 1)) : 0;
        int cMode = instruction.Length >= 5 ? int.Parse(instruction.Substring(instruction.Length - 5, 1)) : 0;
        
        switch (opcode) {
            case 1:
            case 2: {
                bool multiply = opcode == 2;
                int a = aMode == ImmediateMode ? memory[ip + 1] : memory[memory[ip + 1]];
                int b = bMode == ImmediateMode ? memory[ip + 2] : memory[memory[ip + 2]];
                int c = cMode == ImmediateMode ? ip+3 : memory[ip+3];
                if (multiply) memory[c] = a * b;
                else memory[c] = a + b;
                ip += 4;
            } break;
            case 3: {
                memory[memory[ip+1]] = input;
                ip += 2;
            } break;
            case 4: {
                output = memory[memory[ip+1]];
                ip += 2;
            } break;
            case 5:
            case 6: {
                bool checkEqual = opcode == 6;
                int a = aMode == ImmediateMode ? memory[ip + 1] : memory[memory[ip + 1]];
                int b = bMode == ImmediateMode ? memory[ip + 2] : memory[memory[ip + 2]];
                if (checkEqual && a == 0 || !checkEqual && a != 0) ip = b;
                else ip += 3;
            } break;
            case 7:
            case 8: {
                bool checkEqual = opcode == 8;
                int a = aMode == ImmediateMode ? memory[ip + 1] : memory[memory[ip + 1]];
                int b = bMode == ImmediateMode ? memory[ip + 2] : memory[memory[ip + 2]];
                int c = cMode == ImmediateMode ? ip+3 : memory[ip+3];
                if (checkEqual && a == b || !checkEqual && a < b) memory[c] = 1;
                else memory[c] = 0;
                ip += 4;
            } break;
            case 99: {
                return output;
            }
            default: {
                throw new Exception("Halt!");
            }
        }
    }
    
    return output;
}