1.4.20 BitonicSearch

package search;

/**
 * 双调查找
 * @author kuhuf
 * Attention: the array's length must greater than 2 
 * Attention: the array must be ordered
 */
public class BitonicSearch {
    
    public static int find(int[] a, int key){
        int lo = 0;
        int hi = a.length-1;
        int mid = -1;
        while(lo <= hi){
            mid = (lo + hi) / 2;
            if(a[mid] > a[mid - 1]){
                int index = BinarySearch.rank(key, a, lo, mid);
                if(index != -1) return index;
                lo = mid + 1;
            }else if(a[mid] > a[mid + 1]){
                int index = BinarySearch.rank(key, a, mid, hi);
                if(index != -1) return index;
                hi = mid - 1;
            }
        }
        
        
        return -1;
    }
    
    /**
     * 1. 找到极值点（极值点也是用二分法找到的）(extreme point, binary method)
     * 2. 根据极值点将数组分为两部分，分别进行二分搜索，查找key值
     * according to the extreme point, divide the array into two parts
     * use Binary search respectively find the key value
     * @param a
     * @param key
     * @return
     */
    public static int find2(int[] a, int key){
        int lo = 0;
        int hi = a.length-1;
        int mid = -1;
        while(lo <= hi){
            mid = (lo + hi) / 2;
            if(a[mid] > a[mid - 1]){
                lo = mid + 1;
            }else{
                hi = mid - 1;
            }
        }
        
        int left = BinarySearch.rank(key, a, 0, mid);
        int right = BinarySearch.rank(key, a, mid, a.length-1);
        
        return left > right ? left : right;
    }
    
    public static void main(String[] args) {
        int[] a = {-1, 2,3, 4,5};
        
        System.out.println( find2(a, 3) );
        
        
    } 
}