440. K-th Smallest in Lexicographical Order
Given two integers n and k, return the kth lexicographically smallest integer in the range [1, n].
Example 1:
Input: n = 13, k = 2
Output: 10
Explanation: The lexicographical order is [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9], so the second smallest number is 10.
Example 2:
Input: n = 1, k = 1
Output: 1
Constraints:
- 1 <= k <= n <= 109
class Solution {
public int findKthNumber(int n, int k) {
long cur = 1;
while(k > 1) {
long gap = findGap(cur, cur + 1, n);
if(gap <= k - 1) {
k -= gap;
cur = cur + 1;
}
else {
cur = cur * 10;
k -= 1;
}
}
return (int)cur;
}
private long findGap(long a, long b, int n) {
long gap = 0;
while(a <= n) {
gap += Math.min(n + 1, b) - a;
a = a * 10;
b = b * 10;
}
return gap;
}
}