402. Remove K Digits-优快云博客

本文介绍了一个算法问题：如何从一个非负整数中移除k位数，使得剩下的数字尽可能小。通过具体示例展示了该算法的工作原理，并提供了C++实现代码。该算法使用了栈来辅助解决此问题。

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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.

class Solution {
public:
    string removeKdigits(string num, int k) {
        std::vector<int> S;
        std::string result="";
        for(int i=0; i<num.length();i++)
        {
            int number = num[i]-'0';
            while(S.size()!=0&&S[S.size()-1]>number&&k>0)
            {
                S.pop_back();
                k--;
            }
            if(number!=0 || S.size()!=0)
            {
                S.push_back(number);
            }
        }
        while(S.size()!=0&&k>0)
        {
            S.pop_back();
            k--;
        }
        for(int i=0; i<S.size(); i++)
        {
            result.append(1,'0'+S[i]);
        }
        if(result=="")
        {
            result = "0";
        }
        return result;
    }
};