public class Contrast {

    public static void main(String[] args) {
        
        int []x = new int[10000*10000];
        for (int i = 0; i < x.length; i++) {
            x[i] = i+1;
        }
        
        int target = 10000*10000;
        
        long now = System.currentTimeMillis();  // 统计当前时间的方法
        int index = binarySearch(x, 0, x.length-1, target);
        System.out.println("二分查找所需时间:"+(System.currentTimeMillis()-now)+"ms");
        System.out.println(target+"所在位置为："+index);
        
        now = System.currentTimeMillis();
        index = search(x, target);
        System.out.println("顺序查找所需时间:"+(System.currentTimeMillis()-now)+"ms");
    }
    
    /**
     * 二分查找  非递归
     * @param arr
     * @param low
     * @param high
     * @param key
     * @return
     */
    static int binarySearch(int arr[],int low,int high,int key){
        while(low<=high){
            int mid = low + ((high-low) >> 1);   //  (high+low) >>> 1  防止溢出，移位更加高效，同时，每次循环都需要更新
            int midVal = arr[mid];
            
            if (midVal<key) {
                low = mid +1;
            }else if (midVal>key) {
                high = mid - 1;
            }else {
                return mid;    // key found
            }
        }
        return -(low + 1);   // key not found
    }

    /**
     * 顺序查找
     */
    static int search(int arr[],int key){
        for (int i = 0; i < arr.length; i++) {
            if (arr[i]==key) {
                return i;
            }
        }
        return -1;
    }
}