LeetCode-in-Java
440. K-th Smallest in Lexicographical Order
Hard
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
Solution
public class Solution {
public int findKthNumber(int n, int k) {
int curr = 1;
k = k - 1;
while (k > 0) {
int steps = calSteps(n, curr, curr + 1L);
if (steps <= k) {
curr += 1;
k -= steps;
} else {
curr *= 10;
k -= 1;
}
}
return curr;
}
// use long in case of overflow
private int calSteps(int n, long n1, long n2) {
long steps = 0;
while (n1 <= n) {
steps += Math.min(n + 1L, n2) - n1;
n1 *= 10;
n2 *= 10;
}
return (int) steps;
}
}