LeetCode in Kotlin
233. Number of Digit One
Hard
Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.
Example 1:
Input: n = 13
Output: 6
Example 2:
Input: n = 0
Output: 0
Constraints:
0 <= n <= 109
Solution
class Solution {
fun countDigitOne(n: Int): Int {
var ans = 0
var k = n
var cum = 0
var curr10 = 1
while (k > 0) {
val rem = k % 10
val q = k / 10
ans += if (rem == 0) {
q * curr10
} else if (rem == 1) {
q * curr10 + cum + 1
} else {
(q + 1) * curr10
}
k = q
cum += rem * curr10
curr10 *= 10
}
return ans
}
}