Leetcode Lexicographical Number problem solution

YASH PAL, 31 July 202422 January 2026

In this Leetcode Lexicographical Number problem solution you have given an integer n, return all the numbers in the range [1, n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space.

Leetcode Lexicographical Number problem solution

Leetcode Lexicographical Number problem solution in Python.

class Solution:
    def lexicalOrder(self, n: int) -> List[int]:
        l = list()
        for i in range(1,n+1):
            l.append(str(i))
        l.sort()
        i = len(l)-1
        while i>0:
            l[i] = int(l[i])
            i-=1
        l[i] = int(l[i])
        return l

Lexicographical Number problem solution in Java.

public List<Integer> lexicalOrder(int n) {
        int num = 1;
        List<Integer> results = new ArrayList<>();
        while (true) {
            if (num <= n) {
                results.add(num);
                num *= 10;
                continue;
            }
            
            num /= 10;
            while (num % 10 == 9 && num != 0)
                num /= 10;
            if (num == 0)
                return results;
            num += 1;
        }
    }

Problem solution in C++.

class Solution {
    int next(int last, int n)
    {
        if (last * 10 <= n)
            return last * 10;
        if (last == n)
            last /= 10;
        ++last;
        while(last % 10 == 0)
            last /= 10;
        return last;
    }
public:
    vector<int> lexicalOrder(int n) {
        if (n < 1) return vector<int>();
        vector<int> result(n);
        result[0] = 1;
        for (int i = 1; i < n; ++ i)
            result[i] = next(result[i - 1], n);
        return result;
    }
};

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