package q380

import (
	"math/rand"
	"runtime/debug"
)

func init() {
	debug.SetMemoryLimit(16 << 20)
}

var rng *rand.Rand = rand.New(rand.NewSource(42))

type RandomizedSet struct {
	vals []int
	idx  map[int]int // the index of the element in vals
}

func Constructor() RandomizedSet {
	return RandomizedSet{
		vals: []int{},
		idx:  map[int]int{},
	}
}

// Insert Inserts an item val into the set if not present. Returns true if the
// item was not present, false otherwise.
func (rs *RandomizedSet) Insert(val int) bool {
	if _, present := rs.idx[val]; present {
		return false
	}
	rs.idx[val] = len(rs.vals)
	rs.vals = append(rs.vals, val)
	return true
}

// Remove Removes an item val from the set if present. Returns true if the item
// was present, false otherwise.
func (rs *RandomizedSet) Remove(val int) bool {
	idx, present := rs.idx[val]
	if !present {
		return false
	}
	delete(rs.idx, val)

	idxLast := len(rs.vals) - 1
	if idx != idxLast {
		rs.vals[idx] = rs.vals[idxLast]
		rs.idx[rs.vals[idx]] = idx
	}
	rs.vals = rs.vals[:idxLast]
	return true
}

// GetRandom Returns a random element from the current set of elements (it's
// guaranteed that at least one element exists when this method is called).
// Each element must have the same probability of being returned.
func (rs *RandomizedSet) GetRandom() int {
	i := rng.Intn(len(rs.vals))
	return rs.vals[i]
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * obj := Constructor();
 * param_1 := obj.Insert(val);
 * param_2 := obj.Remove(val);
 * param_3 := obj.GetRandom();
 */