func printCombination(arr: [Int], r: Int) {
    trips.removeAll()
    var data: [Int] = []
    for _ in 1...r
    {
        data.append(Int())
    }
    combinationUtil(arr: arr, r: r, index: 0, data: data, i: 0)
}

func combinationUtil(arr: [Int], r: Int, index: Int, data: [Int], i: Int) {
    var data: [Int] = data
    if (index == r)
    {
        for j in 0..<r {
           array.append(data[j])

        }
        return
    }

    if (i >= arr.count) {
        return
    }

    data[index] = arr[i]
    combinationUtil(arr: arr, r: r, index: index + 1, data: data, i: i + 1)
    combinationUtil(arr: arr, r: r, index: index, data: data, i: i + 1)
}
    /* arr[]  ---> Input Array
   r      ---> Size of a combination to be printed
   index  ---> Current index in data[]
   data[] ---> Temporary array to store current combination
   i      ---> index of current element in arr[]     */