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)); } }
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