Question Definition
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.
Java Solution
public String removeKdigits(String num, int k) {
if(k >= num.length()) return "0";
Deque<Integer> res = new ArrayDeque<>();
int n = num.length(), keep = n - k;
for (char c : num.toCharArray()) {
while (k > 0 && !res.isEmpty() && res.peek() > c - '0') {
res.poll();
--k;
}
res.push(c - '0');
}
String result = "";
while(!res.isEmpty())
//System.out.println(res.poll());
result = res.poll() + result;
int i = 0;
for(; i < result.length() - 1 && result.charAt(i) == '0'; i++);
return result.substring(i, Math.min(i + keep, result.length()));
}
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