TOJ 4493 Remove Digits 贪心

4493: Remove Digits

Description

Given an N-digit number, you should remove K digits and make the new integer as large as possible.

Input

The first line has two integers N and K (N不大于500000). 
The next line has a N-digit number with no leading zero.

Output

Output the largest possible integers by removing K digits.

Sample Input 
4 2 
2835 
Sample Output 
85

在一个字符串里找到n-k位的递减数列or前几位递减，一直超时。。。

贪心用栈实现就好的

#include <stdio.h>
char s[500005];
int main()
{
    int n,k,i,j,f=0;
    s[0]=9;
    scanf("%d%d",&n,&k);
    getchar();
    for(i=0; i<n; i++)
    {
        char c;
        c=getchar();
        while(c>s[f])
        {
            if(!k||!f)break;
            k--;
            f--;
        }
        s[++f]=c;
    }
    f-=k;
    s[++f]=0;
    printf("%s",s+1);
    return 0;
}