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.
public class Solution {
// MSP -> Most Significant Position
// The theory is that Reducing digits at MSP is better than reducing digit at LSP
public String removeKdigits(String num, int k) {
// corner case
if (k == num.length())
return "0";
Deque<Character> stack = new LinkedList<>();
int i = 0;
// Starting from MSP -> LSP
for (char c : num.toCharArray()) {
while (k > 0 && !stack.isEmpty() && stack.peek() > c) {
stack.pop();
k--;
}
stack.push(c);
}
// corner case like "11234"
// Remove digits from the end(bcoz they are in inc order)
while (k > 0) {
stack.pop();
k--;
}
// construct the number from the stack
StringBuilder sb = new StringBuilder();
while (!stack.isEmpty())
sb.append(stack.pop());
sb.reverse();
// remove all the 0 at the head
while (sb.length() > 1 && sb.charAt(0) == '0')
sb.deleteCharAt(0);
return sb.toString();
}
}