Monday, June 13, 2016

Count Numbers with Unique Digits

Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.
Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x < 100, excluding [11,22,33,44,55,66,77,88,99])

The trick of this problem is to find the pattern of how to find numbers with unique numbers. The code looks rather easy, but very confusing.

i = 1, 10: nothing is dupliated
i = 2, 9 * 9: the first digit has 9 options (exclude 0), the second digit also has 9 options (exclude the number already taken by the first digit, but include 0).
i = 3, 9 * 9 * 8: first two digits follows rules in i = 2, then the third digit has options that exclude all numbers taken by the previous two digits.
i     , 9 * 9 * 8 *... * (10 - i + 1),  the last digit has options that exclude those already chosen by all previous digits.

The final result is the sum of all results.

public int countNumbersWithUniqueDigits(int n) {
        if (n == 0)
            return 1;
        int rst = 10, count = 9;
        for (int i = 2; i <= n; i++) {
            count *= (10 - i + 1);
            rst += count;
        return rst;

1 comment:

  1. The development of artificial intelligence (AI) has propelled more programming architects, information scientists, and different experts to investigate the plausibility of a vocation in machine learning. Notwithstanding, a few newcomers will in general spotlight a lot on hypothesis and insufficient on commonsense application. IEEE final year projects on machine learning In case you will succeed, you have to begin building machine learning projects in the near future.

    Projects assist you with improving your applied ML skills rapidly while allowing you to investigate an intriguing point. Furthermore, you can include projects into your portfolio, making it simpler to get a vocation, discover cool profession openings, and Final Year Project Centers in Chennai even arrange a more significant compensation.

    Data analytics is the study of dissecting crude data so as to make decisions about that data. Data analytics advances and procedures are generally utilized in business ventures to empower associations to settle on progressively Python Training in Chennai educated business choices. In the present worldwide commercial center, it isn't sufficient to assemble data and do the math; you should realize how to apply that data to genuine situations such that will affect conduct. In the program you will initially gain proficiency with the specialized skills, including R and Python dialects most usually utilized in data analytics programming and usage; Python Training in Chennai at that point center around the commonsense application, in view of genuine business issues in a scope of industry segments, for example, wellbeing, promoting and account.