440 K-th Smallest in Lexicographical Order 字典序的第K小数字
给定整数 n 和 k,找到 1 到 n 中字典序第 k 小的数字。
注意:1 ≤ k ≤ n ≤ 109。
示例 :
输入:
n: 13 k: 2
输出:
10
解释:
字典序的排列是 [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9],所以第二小的数字是 10。
详见:https://leetcode.com/problems/k-th-smallest-in-lexicographical-order/description/
C++:
class Solution { public: int findKthNumber(int n, int k) { int cur = 1; --k; while (k > 0) { long long step = 0, first = cur, last = cur + 1; while (first <= n) { step += min((long long)n + 1, last) - first; first *= 10; last *= 10; } if (step <= k) { ++cur; k -= step; } else { cur *= 10; --k; } } return cur; } };
参考:https://www.cnblogs.com/grandyang/p/6031787.html