RandomizedSet.go

/* https://leetcode.com/problems/insert-delete-getrandom-o1/
Design a data structure that supports all following operations in average O(1) time.

insert(val): Inserts an item val to the set if not already present.
remove(val): Removes an item val from the set if present.
getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.
Example:

// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();

// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);

// Returns false as 2 does not exist in the set.
randomSet.remove(2);

// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);

// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();

// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);

// 2 was already in the set, so return false.
randomSet.insert(2);

// Since 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();
*/

package ldesign

import (
	"math/rand"
)

type RandomizedSet struct {
	tmp    []int
	keys   map[int]int
	length int
}

/** Initialize your data structure here. */
func RandomizedSetConstructor() RandomizedSet {
	return RandomizedSet{tmp: []int{}, keys: make(map[int]int), length: 0}
}

/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
func (this *RandomizedSet) Insert(val int) bool {
	if _, ok := this.keys[val]; ok {
		return false
	}
	this.tmp = append(this.tmp, val) // 永远放在最后
	this.keys[val] = this.length
	this.length++
	return true
}

/** Removes a value from the set. Returns true if the set contained the specified element. */
func (this *RandomizedSet) Remove(val int) bool {
	if idx, ok := this.keys[val]; !ok {
		return false
	} else {
		delete(this.keys, val)
		this.length--
		if idx != this.length {
			this.tmp[idx] = this.tmp[this.length]
			this.keys[this.tmp[idx]] = idx
		}
		this.tmp = this.tmp[0:this.length]
	}
	return true
}

/** Get a random element from the set. */
func (this *RandomizedSet) GetRandom() int {
	return this.tmp[rand.Intn(this.length)]
}

/**
 * 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();
 */