Number of occurrences of the 37 number in the sorted array

Title Description

Count the number of occurrences of a number in a sorted array

Idea 1: The cycle of Violence O (N)

public class Solution {
    public int GETNUMBEROFK (int [] A, int k) {
        int cnt=0;
       for (int i=0;i<a.length;i++)
           if (a[i]==k)
               cnt++;
        return CNT;
    }
}

Idea 2: Using two points to find O (LOGN)

Use the binary search to find the first occurrence of the number of the position and the last occurrence of the position.
2 position difference is the number of times.

Use 2 to find the first K (the number to be asked), take K compared to the middle of the array, if K is large, then go to the second half to find;
If k is small, then go to the first half to find, if equal, to determine whether the current K is not the first time to appear. (if k is equal to the number in front of K, it is not the first occurrence, if K is greater than the number before the K, it is the first occurrence), if K is not the first time, then go to K before continuing to find, if it is the first occurrence, then found the position.

1  Public classSolution {2          Public intGETNUMBEROFK (int[] A,intk) {3             if(a.length==0)return0;4             intf =Getfirstk (A, k);5             intL =Getlstk (a,k);6             if(A[f]==k && a[l]==k)7                 returnL-f+1;8             Else9                 return0;Ten         } One      A         Private intGETFIRSTK (intA[],intk) { -              -             intLo = 0,hi=a.length-1; the             intMid =0; -              while(true) { -                 if(Lo>=hi)returnHi; -Mid = (Hi-lo)/2+Lo; +                  if(k<A[mid]) -Hi=mid-1; +                  Else if(k>A[mid]) { ALo=mid+1; at                 } -                  Else { -                     if(mid-1>=lo&&a[mid-1]==k) -hi = mid-1; -                     Else -                         returnmid;  in                 } -             }        to         } +     Private intGETLSTK (intA[],intk) { -              the             intLo = 0,hi=a.length-1; *             intMID = 0; $              while(true) {Panax Notoginseng                 if(Lo>=hi)returnLo; -Mid = (Hi-lo)/2+Lo; the                  if(k<A[mid]) +Hi=mid-1; A                  Else if(k>A[mid]) { theLo=mid+1; +                 } -                  Else { $                     if(mid+1<=hi&&a[mid+1]==k) $Lo = mid+1; -                     Else -                         returnmid;  the                 } -             }    Wuyi         } the      -      Wu      -}

Number of occurrences of the 37 number in the sorted array