【小米OJ-移除k位得到最小值】栈的应用

 

 

import java.util.*;

public class Main {
    public static void main(String args[]) {
        Scanner scan = new Scanner(System.in);
        String line;
        while (scan.hasNextLine()) {
            line = scan.nextLine().trim();
            // please write your code here
            String str[] = line.split(" ");
            int len = str[0].length();
            int k = Integer.parseInt(str[1]);
            int num[] = new int[len];
            for(int i=0;i<len;i++) num[i] = str[0].charAt(i)-'0';
            // System.out.println("answer");
            System.out.println(Main.removeKdigits(num,k));
        }
    }

    private static String removeKdigits(int []num,int k){
        if(num.length==0||k>=num.length) return "0";
        int i=0;
        int rmnum=0;
        LinkedList<Integer> stack = new LinkedList<>();

        for(;i<num.length;i++){
            while(!stack.isEmpty() && stack.peek()>num[i] && rmnum<k){///判断是否为递减数列，是就出栈，去掉高位
                stack.pop();
                rmnum++;
            }
            if(rmnum>=k) break;
            if(num[i]!=0) stack.push(num[i]);///去掉0位
        }
        while(rmnum<k) {///如果还没删除k位，继续出栈就行
            stack.pop();
            rmnum++;
        }
        String ans="";
        while(!stack.isEmpty()) ans = stack.pop() +ans;///连接字符串
        while(ans.length()==0&&i<num.length&&num[i]==0) i++;///如果出现0开头的字符串，则删除前面的0
        while(i<num.length) {
            ans+=num[i]+"";
            i++;
        }
        if(ans.length()==0) return "0";
        return ans;
    }
}