1346. Check If N and Its Double Exist

題目敘述

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists two indices i and j such that :

• i != j
• 0 <= i, j < arr.length
• arr[i] == 2 * arr[j]

Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]
Output: true
Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]
Output: false
Explanation: In this case does not exist N and M, such that N = 2 * M.

Constraints:

• 2 <= arr.length <= 500
• -10^3 <= arr[i] <= 10^3

Hint 1:

Loop from i = 0 to arr.length, maintaining in a hashTable the array elements from [0, i - 1].

Hint 2:

On each step of the loop check if we have seen the element 2 * arr[i] so far or arr[i] / 2 was seen if arr[i] % 2 == 0.

題目翻譯

解法解析

解法範例

Go

func checkIfExist(arr []int) bool {
    seen := make(map[float64]bool)
    for _, v := range arr {
        V := float64(v)
        if seen[V*2.0] || seen[V/2.0] {
            return true
        }
        seen[V] = true
    }
    return false
}

JavaScript

/**
 * @param {number[]} arr
 * @return {boolean}
 */
var checkIfExist = function (arr) {
    const seen = new Set();
    for (const value of arr) {
        if (seen.has(value * 2) || seen.has(value / 2)) {
            return true;
        }
        seen.add(value);
    }
    return false;
};

Kotlin

class Solution {
    fun checkIfExist(arr: IntArray): Boolean {
        val seen = hashSetOf<Int>()
        arr.forEach { num ->
            if (seen.contains(num * 2)) return true
            if (num % 2 == 0 && seen.contains(num / 2)) return true
            seen.add(num)
        }
        return false
    }
}

PHP

class Solution
{

    /**
     * @param Integer[] $arr
     * @return Boolean
     */
    function checkIfExist($arr)
    {
        $map = [];
        foreach ($arr as $val) {
            if (isset($map[$val * 2]) || ($val % 2 == 0 && isset($map[$val / 2]))) {
                return true;
            }
            $map[$val] = true;
        }
        return false;
    }
}

Python

class Solution:
    def checkIfExist(self, arr: List[int]) -> bool:
        seen = set(arr)
        for value in arr:
            if 2 * value in seen or value / 2 in seen:
                return True
            seen.add(value)
        return False

Rust

impl Solution {
    pub fn check_if_exist(arr: Vec<i32>) -> bool {
        let mut nums = std::collections::HashSet::new();

        for num in arr.into_iter() {
            if ((num as f32 / 2 as f32).fract() == 0.0 && nums.contains(&(num / 2))) || nums.contains(&(num * 2)) {
                return true
            }
            nums.insert(num);
        }

        false
    }
}

Swift

class Solution {
    func checkIfExist(_ arr: [Int]) -> Bool {
        var seen = Set<Int>()
        for num in arr {
            if seen.contains(num * 2) || (num % 2 == 0 && seen.contains(num / 2)) {
                return true
            }
            seen.insert(num)
        }
        return false
    }
}