Counting Elements

April 7, 2020

Introduction

Given an integer array arr, count element x such that x + 1 is also in arr.

If there’re duplicates in arr, count them seperately.

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.

Constraints:

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

Solution

Bool array also works, but this one int array was the first impl. Task is too simple.

func countElements(arr []int) int {
    cache := make([]int, 1002)
    for _, v := range arr {
        cache[v]++
    }
    cnt := 0
    for _, v := range arr {
        if cache[v+1] > 0 {
            cnt++
        }
    }
    return cnt
}

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