OC版二分查找

- (void)viewDidLoad {
    [super viewDidLoad];
    
   NSArray * array1 = @[@1,@2,@3,@4,@5,@6,@7,@9];
    
    int result = [self compare:array1 target:@9];
    //在这里打印结果看是否有相等的值
    NSLog(@"%d",result);
}

- (int)compare:(NSArray *)array target:(int)target{
    
    if (!array.count) {
        return -1;
    }
    
   unsigned int low = 0;
   unsigned int high = array.count - 1;
    
    while (low <= high) {
        //会有一些朋友看到有些人是( low + high ) / 2这样写的,但是这样写有一点不好,就是low+high会出现整数溢出的情况,如果存在溢出,你再除以2也是没有用的,所以不能这么写
        int mid = low + ((high - low)/2);
        
        //第mid项的内容
        int num = [array objectAtIndex:mid];
        
        if (target == num) {
            return low;
        }else if (num > target){
            high = mid - 1;//左边进行查找
        }else{
            low = mid +1;//右边进行查找
        }
    }
    return -1;//返回-1是没找到
}