[剑指Offer][数组]数字在升序数组中出现的次数

题目描述

统计一个数字在升序数组中出现的次数。

 

public class Solution {
    public int GetNumberOfK(int [] array , int k) {
       if(array.length == 0) {
           return 0;
       }
       int result = 0;
       for(int i = 0; i < array.length; i ++) {
           if(array[i] == k) {
               result ++;
           }
       }
       return result;
    }
}

public class Solution {
    public int GetNumberOfK(int[] array , int k) {
       int index = binarySearch(array, k);
        if(index < 0) {
            return 0;
        }
        int count = 1;
        for(int i = index + 1; i < array.length && array[i] == k; i++) {
            count++;
        }
        for(int i = index - 1; i >= 0 && array[i] == k; i --) {
            count++;
        }
        return count;
    }
    
    private int binarySearch(int[] array, int target) {
        int left = 0;
        int right = array.length - 1;
        while(left <= right) {
            int middle = (left + right) / 2;
            if(array[middle] == target) {
                return middle;
            }
            if(array[middle] > target) {
                right = middle - 1;
            }
            if(array[middle] < target) {
                left = middle + 1;
            }
        }
        return -1;
    }
}