# LeetCode - 1291. Sequential Digits
### 題目網址：https://leetcode.com/problems/sequential-digits/
###### tags: `LeetCode` `Medium` `數學` `排列組合` `窮舉`

/*
    -LeetCode format-
    Problem: 1291. Sequential Digits
    Difficulty: Medium
    
    by Inversionpeter
*/



class Solution {
public:
    vector<int> sequentialDigits(int low, int high) {
        int buffer;
        vector <int> answers;
        for (int i = 2; i <= 9; ++i)
            for (int j = i; j <= 9; ++j) {
                buffer = 0;
                for (int k = j - i + 1; k <= j; ++k)
                    buffer = (buffer << 1) + (buffer << 3) + k;
                if (low <= buffer && buffer <= high)
                    answers.push_back(buffer);
            }
        return answers;
    }
};