LeetCode 402 贪心 栈 Remove K Digits

LeetCode 402 贪心 栈 Remove K Digits

LeetCode

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.

代码：

import java.util.LinkedList;
class Solution {    
    public String removeKdigits(String num, int k) {
        LinkedList<Character> s = new LinkedList<>();
        for(int i = 0; i < num.length(); i++){
            while(k > 0 && !s.isEmpty() && s.getLast() > num.charAt(i)){
                s.pollLast();
                k--;
            }
            if(!s.isEmpty() || num.charAt(i) != '0')
                s.add(num.charAt(i));
        }
        while(k > 0){
            s.pollLast();
            k--;
        }
        StringBuilder sb = new StringBuilder();
        for(char tmp : s){
            sb.append(tmp);
        }
        if(sb.toString().equals(""))
            return "0";
        return sb.toString();
    }
}

注意：