Little Henry Case decides that defeating bosses with swords and stuff is boring. Now he's playing the game with a wizard. Of course, he gets stuck on another boss and needs your help again.

In this version, combat still proceeds with the player and the boss taking alternating turns. The player still goes first. Now, however, you don't get any equipment; instead, you must choose one of your spells to cast. The first character at or below 0 hit points loses.

Read the full puzzle.

using System;
using System.Collections.Generic;

namespace AdventOfCode.Y2015.Day22;

[ProblemName("Wizard Simulator 20XX")]
class Solution : Solver {

    public object PartOne(string input) {
        var state0 = Parse(input);
        return BinarySearch(mana => TrySolve(state0.WithManaLimit(mana), false));
    }

    public object PartTwo(string input) {
        var state0 = Parse(input);
        return BinarySearch(mana => TrySolve(state0.WithManaLimit(mana), true));
    }

    int BinarySearch(Func<int, bool> f) {
        var hi = 1;
        while (!f(hi)) {
            hi *= 2;
        }
        var lo = hi / 2;
        var first = false;
        while (hi - lo > 1) {
            var m = (hi + lo) / 2;
            if (!first && f(m)) {
                hi = m;
            } else {
                lo = m;
            }
            first = false;
        }
        return hi;
    }

    bool TrySolve(State state, bool hard) {
        if (hard) {
            state = state.Damage(1);
        }
        state = state.ApplyEffects();
        foreach (var stateT in state.PlayerSteps()) {
            state = stateT.ApplyEffects();
            state = state.BossStep();
            if (state.bossHp <= 0 || state.playerHp > 0 && TrySolve(state, hard)) {
                return true;
            }
        }
        return false;
    }

    State Parse(string input){
        var lines = input.Split("\n");
        return new State {
            playerHp = 50,
            playerMana = 500,
            bossHp = int.Parse(lines[0].Split(": ")[1]),
            bossDamage = int.Parse(lines[1].Split(": ")[1])
        };
    }
}


class State {
    const int missileMana = 53;
    const int drainMana = 73;
    const int shieldMana = 113;
    const int poisonMana = 173;
    const int rechargeMana = 229;

    public int shield;
    public int poison;
    public int recharge;
    public int playerHp;
    public int bossHp;
    public int playerMana;
    public int bossDamage;
    public int usedMana;
    public int playerArmor;
    public int manaLimit;

    public State Dup() {
        return this.MemberwiseClone() as State;
    }

    public State WithManaLimit(int manaLimit) {
        var newState = Dup();
        newState.manaLimit = manaLimit;
        return newState;
    }

    public State ApplyEffects() {
        if (playerHp <= 0 || bossHp <= 0) {
            return this;
        }

        var newState = Dup();
        if (newState.poison > 0) {
            newState.bossHp -= 3;
            newState.poison--;
        }

        if (newState.recharge > 0) {
            newState.playerMana += 101;
            newState.recharge--;
        }

        if (newState.shield > 0) {
            newState.shield--;
            newState.playerArmor = 7;
        } else {
            newState.playerArmor = 0;
        }
        return newState;
    }

    public State Damage(int damage) {
        if (playerHp <= 0 || bossHp <= 0) {
            return this;
        }

        var step = Dup();
        step.playerHp -= damage;
        return step;
    }

    public State BossStep(){
        if (playerHp <= 0 || bossHp <= 0) {
            return this;
        }

        var step = Dup();
        step.playerHp -= Math.Max(1, step.bossDamage - step.playerArmor);
        return step;
    }

    public IEnumerable<State> PlayerSteps() {

        if (playerHp <= 0 || bossHp <= 0) {
            yield return this;
            yield break;
        }
   
        if (playerMana >= missileMana && missileMana + usedMana <= manaLimit) {
            var c = Dup();
            c.playerMana -= missileMana;
            c.usedMana += missileMana;
            c.bossHp -= 4;
            yield return c;
        }

        if (playerMana >= drainMana && drainMana + usedMana <= manaLimit) {
            var c = Dup();
            c.playerMana -= drainMana;
            c.usedMana += drainMana;
            c.bossHp -= 2;
            c.playerHp += 2;
            yield return c;
        }

        if (playerMana >= shieldMana && shield == 0 && shieldMana + usedMana <= manaLimit) {
            var c = Dup();
            c.playerMana -= shieldMana;
            c.usedMana += shieldMana;
            c.shield = 6;
            yield return c;
        }

        if (playerMana >= poisonMana && poison == 0 && poisonMana + usedMana <= manaLimit) {
            var c = Dup();
            c.playerMana -= poisonMana;
            c.usedMana += poisonMana;
            c.poison = 6;
            yield return c;
        }

        if (playerMana >= rechargeMana && recharge == 0 && rechargeMana + usedMana <= manaLimit) {
            var c = Dup();
            c.playerMana -= rechargeMana;
            c.usedMana += rechargeMana;
            c.recharge = 5;
            yield return c;
        }
    }
}

Please ☆ my repo if you like it!