LeetCode-in-Java
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 <= 105numconsists of only digits.numdoes not have any leading zeros except for the zero itself.
Solution
public class Solution {
public String removeKdigits(String num, int k) {
char[] list = new char[num.length()];
int len = num.length() - k;
int top = 0;
for (int i = 0; i < num.length(); i++) {
while (top > 0 && k > 0 && num.charAt(i) < list[top - 1]) {
top--;
k--;
}
list[top++] = num.charAt(i);
}
int number = 0;
while (number < len && list[number] == '0') {
number++;
}
return number == len ? "0" : new String(list, number, len - number);
}
}