402. Remove K Digits

难度: Medium

题目描述

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 <= 105
• num consists of only digits.
• num does not have any leading zeros except for the zero itself.

解题思路

代码实现

解决方案

java

class Solution {
    public String removeKdigits(String num, int k) {
        if (num.length() <= k) {
            return "0";
        }
        LinkedList<Character> stack = new LinkedList<>();
        char[] charArray = num.toCharArray();
        int kTemp = k;
        for (char c : charArray) {
            if (stack.isEmpty()) {
                stack.push(c);
                continue;
            }
            while (!stack.isEmpty() && k > 0 && stack.peek() > c) {

                stack.pop();
                k--;

            }
            stack.push(c);
        }
        while(k!=0){
            stack.pop();
            k--;
        }


        StringBuilder sb = new StringBuilder();
        while (!stack.isEmpty()) {
            sb.append(stack.pop());
        }
        while (sb.length() > 0 && sb.lastIndexOf("0") == sb.length() - 1) {
            sb.deleteCharAt(sb.length() - 1);
        }
        if (sb.length() == 0) {
            return "0";
        }
        return sb.reverse().toString();

    }
}