[Solved] rounding up a number to nearest 9

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You can do:

private int getInventorySize(int max) {
    if (max <= 0) return 9;
    int quotient = (int)Math.ceil(max / 9.0);
    return quotient > 5 ? 54: quotient * 9;
}

Divide the number by 9.0. And taking the ceiling will get you the next integral quotient. If quotient is > 5, then simply return 54, else quotient * 9 will give you multiple of 9 for that quotient.

Some test cases:

// Negative number and 0
System.out.println(getInventorySize(-1));  // 9
System.out.println(getInventorySize(0));   // 9

// max <= 9
System.out.println(getInventorySize(5));   // 9
System.out.println(getInventorySize(9));   // 9

// some middle case 
System.out.println(getInventorySize(43));  // 45

// max >= 54
System.out.println(getInventorySize(54));  // 54
System.out.println(getInventorySize(55));  // 54

10

solved rounding up a number to nearest 9