Given an array of integers `cost` and an integer `target`, return the maximum integer you can paint under the following rules:

- The cost of painting a digit `(i + 1)` is given by `cost[i]` (0-indexed).
- The total cost used must be equal to `target`.
- The integer does not have `0` digits.

Since the answer may be very large, return it as a string. If there is no way to paint any integer given the condition, return `"0"`.

Example 1:

    Input: cost = [4,3,2,5,6,7,2,5,5], target = 9
    Output: "7772"
    Explanation: The cost to paint the digit '7' is 2, and the digit '2' is 3. Then cost("7772") = 2*3+ 3*1 = 9. You could also paint "977", but "7772" is the largest number.
    Digit    cost
      1  ->   4
      2  ->   3
      3  ->   2
      4  ->   5
      5  ->   6
      6  ->   7
      7  ->   2
      8  ->   5
      9  ->   5

Example 2:

    Input: cost = [7,6,5,5,5,6,8,7,8], target = 12
    Output: "85"
    Explanation: The cost to paint the digit '8' is 7, and the digit '5' is 5. Then cost("85") = 7 + 5 = 12.

Example 3:

    Input: cost = [2,4,6,2,4,6,4,4,4], target = 5
    Output: "0"
    Explanation: It is impossible to paint any integer with total cost equal to target.

Constraints:

- `cost.length == 9`
- `1 <= cost[i], target <= 5000`