二分查找的實現

import java.util.*;

/**
 * 二分查找
 * 如果有重複的數字則返回該數字在數組中出現的第一次位置
 * @author Administrator
 *
 */
public class BinarySearch {
	    public int getPos(int[] A, int n, int val) {
	        // write code here
	        int right=n-1;
	        int left=0;
	        int index=(int)((right+left)/2);
	        while(right>=left){
	            index=(int)((right+left)/2);
	            if(A[index]==val){
	            	while(index>=0&&A[index]==val){
	            		index--;
	            	}
	            	return index+1;
	            }
	            else if(A[index]>val){
	                right=index-1;
	            }
	            else if(A[index]<val){
	                left=index+1;
	            }
	        }
	        return -1;
	        
	    }
	    public int getPosRecursion(int[] A, int begin,int end, int val){
	    	int right=end;
	        int left=begin;
	        int index=(int)((right+left)/2);
	        if(end<begin){
	        	return -1;
	        }
	        else if(A[index]==val){
	        	while(index>=0&&A[index]==val){
	        		index--;
	        	}	     
	        	return index+1;
	        }
	        else if(A[index]>val){
	        	return getPosRecursion(A, begin, index-1,val);
	        }
	        else{
	        	return getPosRecursion(A, index+1, end,val);
	        }
	    }  
	  


    public static void main(String[] args) {
		int a[]={1,3,3,3,3,6,7,8,9};
		int b=new BinarySearch().getPos(a, 9, 3);
		int c=new BinarySearch().getPosRecursion(a,0,8,3);
		System.out.println(b+" "+c);
	}
}