急！0分求调！在线等！

#include<bits/stdc++.h>
using namespace std;
int q , n , x , len;
bool flag;
string s;
struct node{
    int st , ed , used;
    friend bool operator<(node x , node y) {
        if (x.used == y.used) return x.st < y.st;
        return x.used > y.used;
    }
}a[2000005];
int main() {
    scanf("%d %d", &q , &n);
    while(q --) {
        cin >> s;
        if (s == "alloc") {
            scanf("%d", &x);
            sort(a + 1 , a + len + 1);
            if (flag) {
                int L = a[1].ed - a[1].st + 1;
                a[1].st = 1;
                a[1].ed = L;
                for (int i = 2 ; i <= len ; i ++) {
                    if (!a[i].used) break;
                    int L = a[i].ed - a[i].st + 1;
                    a[i].st = a[i - 1].ed + 1;
                    a[i].ed = a[i].st + L - 1; 
                }
                flag = 0;
            }
            int last = 0 , tmp = -1;
            for (int i = 1 ; i <= len ; i ++) {
                if (a[i].used) last = i;
                if (!a[i + 1].used) break;
                if (a[i + 1].st - a[i].ed - 1 >= x) {
                    tmp = i;
                    break;
                }
            }
            if (a[1].st - 1 >= x) tmp = 0;
            if (n - a[last].ed >= x && tmp == -1) tmp = last;
            if (tmp == -1) {
                puts("NULL");
                continue;
            }
            a[++ len].st = a[tmp].ed + 1;
            a[len].used = 1;
            a[len].ed = a[len].st + x - 1;
            printf("%d\n", len);
        } else if (s == "erase") {
            scanf("%d", &x);
            if (!a[x].used) {
                puts("ILLEGAL_ERASE_ARGUMENT");
                continue;
            } 
            a[x].used = 0;
        } else flag = 1;
    }
    return 0;
}

基本思路：

对于每次插入操作，先对当前存储器进行排序，找到能够满足条件的空位并插入，特判第 1 个和最后 1 个
对于 defragment 操作，留到插入操作的时候再处理
对于 erase 操作，直接标记已被删除