HDU2871 Memory Control 线段树区间合并

题目大意为给定一段内存快，要求根据命令输出正确的答案。

New x    申请长度为x的空白内存的首地址，如果不满足输出Reject New
Free x    释放包含x节点的内存块，注意该内存块为一个New操作所确定的区域，即不必要将物理相邻的内存块视作一个内存块
Get x     得到从左到右的第x个内存块 
Reset     重置总区间

针对这些要求，设定一棵线段树，每个节点保留左，右连续空白段，以及区间总长。这样便能够处理New命令，而Free以及Get命令则用vector保留，用二分搜索优化。

代码如下：

#include <cstdio>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#define MAXN 50000
using namespace std;

struct 
{
    int l, r;
    int lmax, rmax, max, cover;
}seg[MAXN*4];

struct Node
{
    int s, e;
}info;

void up(int f)
{
    seg[f].lmax = seg[f<<1].lmax;
    seg[f].rmax = seg[f<<1|1].rmax;
    if (seg[f<<1].cover == 0)
        seg[f].lmax += seg[f<<1|1].lmax;
    if (seg[f<<1|1].cover == 0)
        seg[f].rmax += seg[f<<1].rmax;
    seg[f].max = max(seg[f<<1].max, seg[f<<1|1].max);
    seg[f].max = max(seg[f].max, seg[f<<1].rmax+seg[f<<1|1].lmax);
    if (seg[f<<1].cover == seg[f<<1|1].cover)
        seg[f].cover = seg[f<<1].cover;
    else
        seg[f].cover = -1;
}

void build(int f, int l, int r)
{
    int mid = l+r >> 1;
    seg[f].l = l, seg[f].r = r;
    seg[f].lmax = seg[f].rmax = seg[f].max = r-l+1;
    seg[f].cover = 0;
    if (r > l)
    {
        build(f<<1, l, mid);
        build(f<<1|1, mid+1, r);
    }
}

void modify(int f, int l, int r, int val)
{
    int mid = seg[f].l+seg[f].r >> 1;
    if (seg[f].l == l && r == seg[f].r)
    {
        seg[f].cover = val;
        if (val == 1)  // 如果是占用命令
            seg[f].lmax = seg[f].rmax = seg[f].max = 0;
        else
            seg[f].lmax = seg[f].rmax = seg[f].max = r-l+1;
    }
    else if (seg[f].r > seg[f].l)
    {
        if (seg[f].cover == 0)
        { // lazy 操作  相当于格式化一般的向下更新
            seg[f<<1].cover = seg[f<<1|1].cover = 0;
            seg[f<<1].lmax = seg[f<<1].r-seg[f<<1].l+1;
            seg[f<<1].rmax = seg[f<<1].r-seg[f<<1].l+1;
            seg[f<<1].max = seg[f<<1].r-seg[f<<1].l+1;
            seg[f<<1|1].lmax = seg[f<<1|1].r-seg[f<<1|1].l+1;
            seg[f<<1|1].rmax = seg[f<<1|1].r-seg[f<<1|1].l+1;
            seg[f<<1|1].max = seg[f<<1|1].r-seg[f<<1|1].l+1;
            seg[f].cover = -1;
        }
        else if (seg[f].cover == 1)
        {
            seg[f<<1].cover = seg[f<<1|1].cover = 1;
            seg[f<<1].lmax = 0;
            seg[f<<1].rmax = 0;
            seg[f<<1].max = 0;
            seg[f<<1|1].lmax = 0;
            seg[f<<1|1].rmax = 0;
            seg[f<<1|1].max = 0;
            seg[f].cover = -1;
        }
        if (r <= mid)
            modify(f<<1, l, r, val);
        else if (l > mid)
            modify(f<<1|1, l, r, val);
        else
        {
            modify(f<<1, l, mid, val);
            modify(f<<1|1, mid+1, r, val);
        }
        up(f);
    }
}

int query(int f, int size)
{
    int mid = seg[f].l+seg[f].r >> 1;
    if (seg[f].max < size)
        return 0;
    else if (seg[f].r > seg[f].l)
    {
        if (seg[f].lmax >= size)
        {
            return seg[f].l;
        }
        else if (seg[f<<1].max >= size)
            return query(f<<1, size);
        else if (seg[f<<1].rmax+seg[f<<1|1].lmax >= size)
            return seg[f<<1].r-seg[f<<1].rmax+1;
        else
            return query(f<<1|1, size);
    }
}

int bsearch(int pos, vector<Node>&v, int way)
{
    int l = 0, r = v.size()-1;
    while (l <= r)
    {
        int mid = l+r >> 1; 
        if (pos > v[mid].s)
            l = mid + 1;
        else if (pos < v[mid].s)
            r = mid - 1;
        else if (way == 1)
            return mid;
    }
    if (way == 0)
        return l;
    else 
        return r;
}

int main()
{
    int N, M, x, loc;
    char op[10];
    while (scanf("%d %d", &N, &M) == 2)
    {
        build(1, 1, N);
        vector<Node>v;
        vector<Node>::iterator it;
        while (M--)
        {
            scanf("%s", op);
            if (op[0] == 'R')
            {
                seg[1].lmax = seg[1].rmax = seg[1].max = N;
                seg[1].cover = 0;
                v.clear();
                puts("Reset Now");
            }
            else if (op[0] == 'N')
            {
                scanf("%d", &x);
                int pos = query(1, x);
                if (pos == 0)
                    puts("Reject New");
                else
                {
                    printf("New at %d\n", pos); 
                    modify(1, pos, pos+x-1, 1);
                    it = v.begin()+bsearch(pos, v, 0);
                    info.s = pos, info.e = pos+x-1;
                    v.insert(it, info);
                }
            }
            else if (op[0] == 'F')
            { 
                scanf("%d", &x);
                loc = bsearch(x, v, 1);
                if (loc == -1)
                    puts("Reject Free"); 
                else
                {
                    it = v.begin()+loc;
                    if (x >= it->s && x <= it->e)
                    {
                        printf("Free from %d to %d\n", it->s, it->e);
                        modify(1, it->s, it->e, 0);
                        v.erase(it);
                    }
                    else
                        puts("Reject Free");
                }
            }
            else
            {
                scanf("%d", &x);
                if (x > v.size())
                    puts("Reject Get");
                else 
                    printf("Get at %d\n", v[x-1].s);
            }
        }
        puts("");
    }
    return 0;
}