1.分清指針的邊界值意義,採用兩種不同的邊界值指針進行二分搜索
二分查找適合有序數組的查找,每次與數組的中間元素對比,小的話,左半部分查找,大的話右半部分查找
public class BinarySearch<T extends Comparable> {
/**
* 二分查找
* @param arr
* @param n
* @param target
* @return
*/
public int binarySearchTarget(T arr[],int n,T target){
int l=0,r=n-1;//邊界設置,[l……r]的範圍裏找target
while(l<=r){//l==r,[l……l]依然有效
int mid=l+(r-l)/2;
if(arr[mid].compareTo(target)==0)
return mid;
else if(target.compareTo(arr[mid])>0){
l=mid+1;//[mid+1,r]
}
else
r=mid-1;//[l,mid-1]
}
return -1;
}
public int binarySearchTarget2(T arr[],int n,T target){
int l=0,r=n;//邊界設置,[l……r)的範圍裏找target
while(l<r){//l==r,[l……l)無效,[42,43)
int mid=l+(r-l)/2;
if(arr[mid].compareTo(target)==0)
return mid;
else if(target.compareTo(arr[mid])>0){
l=mid+1;//[mid+1...r)
}
else
r=mid;//[l,mid)
}
return -1;
}
public static void main(String[] args) {
int n = new BinarySearch<Integer>().binarySearchTarget(new Integer[]{1,3,4,5,8},5,1);
System.out.println(n);
}
}