poj2887

线段树

这种每次在第几个位置插入元素的题，都可以用线段树，从最后一次插入开始来查找每次插入的元素的最终位置。

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#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define maxl 2000005
#define maxn 2005

struct Elem
{
    bool cmd;
    int p;
    char ch;
    int pos;
} elem[maxn];

struct Node
{
    Node *pl;
    Node *pr;
    int lnum, rnum, l, r;
} tree[maxl * 3];

char st1[maxl], st[maxl];
int n, len, ncount;

void input()
{
    scanf("%s%d", st1, &n);
    len = strlen(st1);
    for (int i = 0; i < n; i++)
    {
        char st[5];
        scanf("%s", st);
        if (st[0] == 'I')
        {
            elem[i].cmd = true;
            scanf("%s%d", st, &elem[i].p);
            len++;
            if (elem[i].p > len)
                elem[i].p = len;
            elem[i].ch = st[0];
        }
        else
        {
            elem[i].cmd = false;
            scanf("%d", &elem[i].p);
        }
    }
}

void build_tree(Node *proot, int l, int r)
{
    int mid = (l + r) / 2;
    proot->lnum = mid - l + 1;
    proot->rnum = r - mid;
    proot->l = l;
    proot->r = r;
    if (l == r)
        return;
    ncount++;
    proot->pl = tree + ncount;
    ncount++;
    proot->pr = tree + ncount;
    build_tree(proot->pl, l, mid);
    build_tree(proot->pr, mid + 1, r);
}

int query(Node *proot, int a)
{
    if (proot->l == proot->r)
        return proot->l;
    if (a > proot->lnum)
        return query(proot->pr, a - proot->lnum);
    return query(proot->pl, a);
}

void update(Node *proot, int pos, int a)
{
    if (proot->l == proot->r)
        return;
    int mid = (proot->l + proot->r) / 2;
    if (pos > mid)
    {
        proot->rnum += a;
        update(proot->pr, pos, a);
    }
    else
    {
        proot->lnum += a;
        update(proot->pl, pos, a);
    }
}

void work()
{
    memset(st, 0, sizeof(st));
    for (int i = n - 1; i >= 0; i--)
        if (elem[i].cmd)
        {
            elem[i].pos = query(tree, elem[i].p);
            st[elem[i].pos] = elem[i].ch;
            update(tree, elem[i].pos, -1);
        }
    int j = 0;
    for (int i = 1; i <= len; i++)
        if (!st[i])
            st[i] = st1[j++];
    for (int i = 0; i < n; i++)
        if (elem[i].cmd)
            update(tree, elem[i].pos, 1);
        else
            printf("%c\n",st[query(tree, elem[i].p)]);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    input();
    ncount = 0;
    build_tree(tree, 1, len);
    work();
    return 0;
}