def wave( arr ):
        size=len(arr)
        
        for index in range(0,size,2):
            if((index > 0) and (arr[index-1] > arr[index])):
                arr[index-1] , arr[index] = arr[index] , arr[index-1]
                
            if((index < size-1) and (arr[index] < arr[index+1])):
               arr[index] , arr[index+1] = arr[index+1] , arr[index]
            
        return arr