https://oj.leetcode.com/problems/search-for-a-range/就是一个二分查找，没事练练手
1 public class Solution { 2 public int[] searchRange(int[] A, int target) { 3 int a[]=new int[2]; 4 int ans=bSearch(A,target); 5 if(ans==-1) 6 { 7 a[0]=-1; 8 a[1]=-1; 9 return a; 10 11 } 12 else 13 { 14 int beg=ans; 15 int end=ans; 16 while(beg>=0&&(A[beg]==A[ans])) 17 { 18 beg--; 19 20 } 21 while(end<A.length&&(A[end]==A[ans])) 22 { 23 end++; 24 } 25 a[0]=beg+1; 26 a[1]=end-1; 27 return a; 28 29 } 30 31 32 33 } 34 public int bSearch(int[] A,int target) 35 { 36 int low=0; 37 int high=A.length-1; 38 while(low<=high) 39 { 40 int mid =(low+high)/2; 41 if(A[mid]==target) 42 { 43 return mid; 44 45 } 46 else if(A[mid]>target) 47 { 48 49 50 high=mid-1; 51 52 } 53 else 54 { 55 low=mid+1; 56 } 57 58 59 60 } 61 62 return -1; 63 } 64 65 66 67 }
2.另外一种二分查找 beg=0 end=len; end指向的是最后一个元素的后面，
1 public class Solution { 2 public int[] searchRange(int[] A, int target) { 3 int a[]=new int[2]; 4 int ans=bSearch(A,target); 5 if(ans==-1) 6 { 7 a[0]=-1; 8 a[1]=-1; 9 return a; 10 11 } 12 else 13 { 14 int beg=ans; 15 int end=ans; 16 while(beg>=0&&(A[beg]==A[ans])) 17 { 18 beg--; 19 20 } 21 while(end<A.length&&(A[end]==A[ans])) 22 { 23 end++; 24 } 25 a[0]=beg+1; 26 a[1]=end-1; 27 return a; 28 29 } 30 31 32 33 } 34 public int bSearch(int[] A,int target) 35 { 36 int low=0; 37 int high=A.length; 38 while(low<high) //low<high不能等于 39 { 40 int mid =(low+high)/2; 41 if(A[mid]==target) 42 { 43 return mid; 44 45 } 46 else if(A[mid]>target) 47 { 48 49 50 high=mid; 51 52 } 53 else 54 { 55 low=mid+1; 56 } 57 58 59 60 } 61 62 return -1; 63 } 64 65 66 67 }
3.第一种方法的递归方式
1 public class Solution { 2 public int[] searchRange(int[] A, int target) { 3 int a[]=new int[2]; 4 int ans=bSearch(A,target,0,A.length); 5 if(ans==-1) 6 { 7 a[0]=-1; 8 a[1]=-1; 9 return a; 10 11 } 12 else 13 { 14 int beg=ans; 15 int end=ans; 16 while(beg>=0&&(A[beg]==A[ans])) 17 { 18 beg--; 19 20 } 21 while(end<A.length&&(A[end]==A[ans])) 22 { 23 end++; 24 } 25 a[0]=beg+1; 26 a[1]=end-1; 27 return a; 28 29 } 30 31 32 33 } 34 public int bSearch(int[] A,int target,int low,int high) 35 { 36 37 while(low<high) 38 { 39 int mid =(low+high)/2; 40 if(A[mid]==target) 41 { 42 return mid; 43 44 } 45 else if(A[mid]>target) 46 { 47 48 49 bSearch(A,target,low,mid); 50 51 } 52 else 53 { 54 bSearch(A,target,mid,high); 55 } 56 57 58 59 } 60 61 return -1; 62 } 63 64 65 66 }