Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.
Note:
- The length of num is less than 10002 and will be ≥ k.
- The given num does not contain any leading zero.
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.
Solution:
class Solution {
public String removeKdigits(String num, int k) {
int size = num.length();
if (k == size) {
return "0";
}
Stack<Character> stack = new Stack<>();
int counter = 0;
// 1432219 // 1219
// 439
// stack [1,3]
// counter = 2
// k = 2
// size = 7
while (counter < size) {
while (k > 0 && !stack.isEmpty() && stack.peek() > num.charAt(counter)) {
stack.pop();
k--;
}
stack.push(num.charAt(counter));
counter++;
}
while (k > 0) {
stack.pop();
k--;
}
StringBuilder sb = new StringBuilder();
while (!stack.isEmpty()) {
sb.append(stack.pop());
}
sb.reverse();
while (sb.length() > 1 && sb.charAt(0) == '0') {
sb.deleteCharAt(0);
}
return sb.toString();
}
}