402.Remove-K-Digits
402. Remove K Digits
题目地址
https://leetcode.com/problems/remove-k-digits/
题目描述
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
Approach #1 Greedy with Stack
class Solution {
public String removeKdigits(String num, int k) {
LinkedList<Character> stack = new LinkedList<Character>();
for (char digit: num.toCharArray()) {
// 单调递增栈
while (stack.size() > 0 && k > 0 && stack.peekLast() > digit) {
stack.removeLast();
k -= 1;
}
stack.addLast(digit);
}
for (int i = 0; i < k; i++) {
stack.removeLast();
}
StringBuilder ret = new StringBuilder();
boolean leadingZero = true;
for (char digit: stack) {
if (leadingZero && digit == '0') continue;
leadingZero = false;
ret.append(digit);
}
if (ret.length() == 0) return "0";
return ret.toString();
}
}
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