402. Remove K Digits
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.
- Stack
public String removeKdigits(String num, int k) {
if(k == num.length()) return "0";
LinkedList<Character> stack = new LinkedList<>();
int cnt = 0;
for(int i = 0; i < num.length(); i++) {
char c = num.charAt(i);
while(cnt < k && !stack.isEmpty() && stack.peek() > c) {
stack.pop();
cnt++;
}
stack.push(c);
}
while(cnt < k) {
stack.removeFirst();
cnt++;
}
StringBuilder result = new StringBuilder();
for(char c : stack) result.insert(0, c);
int j = 0;
while(j < result.length() && result.charAt(j) == '0') j++;
if(j == result.length()) return "0";
return result.toString().substring(j);
}