[贪心] COJ 1236 删数游戏

每次查找第一个降序的首字符，如果不存在就删除结尾字符，链表，O(n)。

# include <cstdio>
# include <iostream>

using namespace std;

struct node
{
    char ch;
    node *pre, *next;
};

void b(node *head, char *s)
{
    head->ch = s[0];
    node *tmp = head;
    for (int i = 0; s[i]; ++i)
    {
        node *cur = new node;
        cur->ch = s[i+1];
        tmp->next = cur;
        cur->pre  = tmp;
        cur->next = NULL;
        tmp = cur;
    }
}

node* d(node *head, int n)
{
    node *tmp = head;
    while (n)
    {
        if ((tmp->ch) > (tmp->next->ch))
        {
            --n;
            if (tmp == head)
            {
                head = head->next;
                head->pre = NULL;
                delete tmp;
                tmp = head;
            }
            else
            {
                node *cur = tmp->pre;
                tmp->pre->next = tmp->next;
                tmp->next->pre = tmp->pre;
                delete tmp;
                tmp = cur;
            }
        }
        else tmp = tmp->next;
    }
    return head;
}

void p(node *head)
{
    node *cur = head;
    while (cur->ch == '0') cur = cur->next;
    if (cur->ch == '\0') puts("0");
    else
    {
        while (cur->ch != '\0')
        {
            putchar(cur->ch);
            cur = cur->next;
        }
        putchar('\n');
    }
}

void k(node *p)
{
    if (p->next)
    {
        k(p->next);
        delete p;
    }
}

int ss;
char nn[2005];

void solve(void)
{
    node *head = new node;
    head->pre = NULL;
    head->next = NULL;
    b(head, nn);
    head = d(head, ss);
    p(head);
    k(head);
}

int main()
{    
    while (~scanf("%s%d", nn, &ss))
        solve();
    
    return 0;
}