LeetCode 1012: Numbers With Repeated Digits Solution

Master LeetCode problem 1012 (Numbers With Repeated Digits), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1012. Numbers With Repeated Digits

Hard

Math Dynamic Programming

Problem Explanation

Explanation

To solve this problem, we can iterate through the range of numbers from 1 to n and check if each number has any repeated digits. We can use a helper function to check if a number has repeated digits. This helper function can be implemented using a set to keep track of the digits we have seen so far. If we encounter a digit that is already in the set, then that means the number has repeated digits.

We will count the numbers that have repeated digits and return this count as the final result.

Algorithm:

Initialize a variable count to 0 to keep track of the numbers with repeated digits.
Iterate through the numbers from 1 to n.
For each number, check if it has repeated digits using the helper function.
If the number has repeated digits, increment the count.
Return the final count as the result.

Time Complexity

The time complexity of this algorithm is O(n * log(n)), where n is the input number. This is because we are iterating through n numbers and checking each number for repeated digits takes O(log(n)) time complexity.

Space Complexity

The space complexity of this algorithm is O(log(n)) due to the use of the set to store the digits of each number.

Solution Code

class Solution {
    public int numDupDigitsAtMostN(int n) {
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (hasRepeatedDigits(i)) {
                count++;
            }
        }
        return count;
    }
    
    private boolean hasRepeatedDigits(int num) {
        Set<Integer> seen = new HashSet<>();
        while (num > 0) {
            int digit = num % 10;
            if (seen.contains(digit)) {
                return true;
            }
            seen.add(digit);
            num /= 10;
        }
        return false;
    }
}

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