30-Day Leetcoding Challenge Day7

三种解法：

第一种是在数组中查找O(n^2)

第二种是在HashSet中查找O(n)

第三种是在有序数组中查找O(nlogn)

JAVA

class Solution {
    public int countElements(int[] arr) {
        int res = 0;
        for(int i = 0; i < arr.length; i++){
            int cur = arr[i]+1;
            for(int j = 0; j < arr.length; j++){
                if(cur == arr[j]){
                    res++;
                    break; //!!!bug
                }
            }
        }
        return res;
    }
}

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

class Solution {
    public int countElements(int[] arr) {
        Arrays.sort(arr);
        int res = 0;
        int length = 1;
        for(int i = 1; i < arr.length; i++){
            if(arr[i-1] != arr[i]){
                if(arr[i-1] + 1 == arr[i]){
                    res += length;
                }
                length = 0;
            }
            length++;
        }
        return res;
    }
}

Python3

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

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

class Solution:
    def countElements(self, arr: List[int]) -> int:
        arr.sort()
        res = 0
        length = 1
        for i in range(1, len(arr)):
            if arr[i-1] != arr[i]:
                if arr[i-1] + 1 == arr[i]:
                    res += length
                length = 0
            length += 1
        return res