README_EN.md

1426. Counting Elements

中文文档

Description

Given an integer array arr, count how many elements x there are, such that x + 1 is also in arr. If there are duplicates in arr, count them separately.

 

Example 1:

Input: arr = [1,2,3]
Output: 2
Explanation: 1 and 2 are counted cause 2 and 3 are in arr.

Example 2:

Input: arr = [1,1,3,3,5,5,7,7]
Output: 0
Explanation: No numbers are counted, cause there's no 2, 4, 6, or 8 in arr.

Example 3:

Input: arr = [1,3,2,3,5,0]
Output: 3
Explanation: 0, 1 and 2 are counted cause 1, 2 and 3 are in arr.

Example 4:

Input: arr = [1,1,2,2]
Output: 2
Explanation: Two 1s are counted cause 2 is in arr.

Example 5:

Input: arr = [1,1,2]
Output: 2
Explanation: Both 1s are counted because 2 is in the array.

 

Constraints:

• 1 <= arr.length <= 1000
• 0 <= arr[i] <= 1000

Solutions

Python3

class Solution:
    def countElements(self, arr: List[int]) -> int:
        s = set(arr)
        res = 0
        for num in arr:
            if num + 1 in s:
                res += 1
        return res

Java

class Solution {
    public int countElements(int[] arr) {
        Set<Integer> s = new HashSet<>();
        for (int num : arr) {
            s.add(num);
        }
        int res = 0;
        for (int num : arr) {
            if (s.contains(num + 1)) {
                ++res;
            }
        }
        return res;
    }
}

C++

class Solution {
public:
    int countElements(vector<int>& arr) {
        unordered_set<int> s;
        for (int num : arr) s.insert(num);
        int res = 0;
        for (int num : arr)
            if (s.count(num + 1)) ++res;
        return res;
    }
};

Go

func countElements(arr []int) int {
	s := make(map[int]bool)
	for _, num := range arr {
		s[num] = true
	}
	res := 0
	for _, num := range arr {
		if s[num+1] {
			res++
		}
	}
	return res
}

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