package Search;
public class biSearch {
//标准的二分查找
public static int stdBiSearch(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<array[mid]) right=mid-1;
else if(keyValue>array[mid]) left=mid+1;
else return mid;
}
return -1;
}
//（二分法）查找第一个小于keyValue的元素
public static int BiSearchToFindFirstSmaller(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<=array[mid]) right=mid-1;
else left=mid+1;
}
return right;
}
//（二分法）查找第一个大于等于keyValue的元素
public static int BiSearchToFindFirstBiggerorEqual(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<=array[mid]) right=mid-1;
else left=mid+1;
}
return left;
}
//（二分法）查找第一个最后一个小于等于keyValue的元素
public static int BiSearchToFindLastSmallerorEqual(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<array[mid]) right=mid-1;
else left=mid+1;
}
return right;
}
//（二分法）查找第一个第一个大于keyValue的元素
public static int BiSearchToFindFirstBigger(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<array[mid]) right=mid-1;
else left=mid+1;
}
return left;
}
//（二分法）查找第一个第一个等于keyValue的元素
public static int BiSearchToFindFirst(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<=array[mid]) right=mid-1;
else left=mid+1;
}
//array[right]<keyValue<=array[left]
if(left<length&&array[left]==keyValue) return left;
else return -1;
}
//（二分法）查找第一个最后一个等于keyValue的元素
public static int BiSearchToFindLast(int[] array,int keyValue) {
int length=array.length;
int left=0,right=length-1;
while(left<=right){
int mid=(left+right)/2;
if(keyValue<array[mid]) right=mid-1;
else left=mid+1;
}
//array[right]<=keyValue<array[left]
if(right>=0&&array[right]==keyValue) return right;
else return -1;
}
//测试样例
public static void main(String[] args) {
int[] a=new int[]{0,1,2,2,2,5,6};
System.out.println(BiSearchToFindLast(a, 2));
}
}一张图帮助理解：