二分法查找

     /**
     * 二分法查找 找不到返回-1
     * @author yangzi
     * 
     */
     public class TwoFind {

         public static int twoFind(int ia, int[] arr, int left, int right) {
    
            if (left > right) {
        return -1;
    }
    if (arr[(left + right) / 2] == ia) {
        return (left + right) / 2;
    }
    if (arr[(left + right) / 2] < ia) {         
        return twoFind(ia, arr, (left + right) / 2 + 1, right);
    }
    if (arr[(left + right) / 2] > ia) {
        return twoFind(ia, arr, left, (left + right) / 2 - 1);
    }
    return -1;

    }

    public static void main(String[] args) {
    //      下标    0                    7  8                          15
    int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };
    int ia = 16;
    int left = 0;
    int right = arr.length - 1;
    // 调用
    System.out.println(twoFind(ia, arr, left, right));
    }

}