LeetCode in Kotlin

402. Remove K Digits

Medium

Given string num representing a non-negative integer num, and an integer k, return the smallest possible integer after removing k digits from num.

Example 1:

Input: num = “1432219”, k = 3

Output: “1219”

Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.

Example 2:

Input: num = “10200”, k = 1

Output: “200”

Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.

Example 3:

Input: num = “10”, k = 2

Output: “0”

Explanation: Remove all the digits from the number and it is left with nothing which is 0.

Constraints:

• 1 <= k <= num.length <= 105
• num consists of only digits.
• num does not have any leading zeros except for the zero itself.

Solution

@Suppress("NAME_SHADOWING")
class Solution {
    fun removeKdigits(num: String, k: Int): String {
        var k = k
        val list = CharArray(num.length)
        val len = num.length - k
        var top = 0
        for (i in 0 until num.length) {
            while (top > 0 && k > 0 && num[i] < list[top - 1]) {
                top--
                k--
            }
            list[top++] = num[i]
        }
        var number = 0
        while (number < len && list[number] == '0') {
            number++
        }
        return if (number == len) "0" else String(list, number, len - number)
    }
}

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