一种是递归的，一种是非递归的

int binarySeach(int a[],int low,int high,int findNum)

{

    if(low>high) {

        return-1;

    }

    int mid = (low + high) /2;

    if(findNum > a[mid]) {

        low = mid +1;

        return binarySeach(a, low, high, findNum);

    }else if(findNum < a[mid])

    {

        high = mid -1;

        return binarySeach(a, low, high, findNum);

    }else

    {

        return mid;

    }

}

int binarySeach2(int a[],int low,int high,int findNum)

{

    while(low<=high) {

        int mid = (low + high) /2;

        if(findNum > a[mid]) {

            low = mid +1;

        }else if(findNum < a[mid])

        {

            high = mid -1;

        }else

        {

            return  mid;

        }

    }

    return  -1;

}

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view.

    int a[] = {1,3,4,6,8,10,12,13,14,18,22,25,28,30,33,37,42,55,76,88,199,211};

    int result =binarySeach2(a,0,21,199);

    NSLog(@"result=%d",result);

}