題目描述

統計一個數字在升序陣列中出現的次數。

示例 1

輸入

[1,2,3,3,3,3,4,5],3

返回值

4

核心程式碼實現

public class Solution {
    public int GetNumberOfK(int [] array , int k) {
        if(array == null || array.length == 0){
            return 0;
        }
        
        int counts = 0;
        /*方法一
       for(int i = 0; i < array.length; i++){
           if(k == array[i]){
               counts++;
           }
       }
        return counts;
        */
        
        //方法二：二分法
        int low = 0, mid = 0, high = array.length - 1;
        while(low < high){
            mid = low + (high - low)/2;
            if(array[mid] < k){
                low = mid + 1;
            }else if(array[mid] > k){
                high = mid - 1;
            }else{
                break;
            }
        }
        for(int i = low; i <= high; i++){
            if(array[i] == k){
                counts++;
            }
        }
        return counts;
    }
}