HDU 1540 Tunnel Warfare （线段树区间合并）

题意: 1-2-3-...-n连成一条链, 三种操作

           D: 毁掉x   R: 恢复上次毁掉的 Q:查询与x直接相连或者间接相邻的数量(包括自己)

分析: 线段树求区间连续最大和, 经典题目 维护区间从左端点开始最大连续和lsum, 同理rsum

          查询的时候 查看当前是否在子区间的rsum和lsum 范围内 是的话 答案就是它 找不到就是0

          用栈来维护被摧毁的城市

代码:

//
//  Created by TaoSama on 2015-09-17
//  Copyright (c) 2015 TaoSama. All rights reserved.
//
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <algorithm>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <string>
#include <set>
#include <vector>

using namespace std;
#define pr(x) cout << #x << " = " << x << "  "
#define prln(x) cout << #x << " = " << x << endl
const int N = 5e4 + 10, INF = 0x3f3f3f3f, MOD = 1e9 + 7;

int n, q;
int lsum[N << 2], rsum[N << 2], stk
, top;

#define root 1, n, 1
#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1

void push_up(int rt, int m) {
lsum[rt] = lsum[rt << 1];
rsum[rt] = rsum[rt << 1 | 1];
if(lsum[rt << 1] == m - (m >> 1)) lsum[rt] += lsum[rt << 1 | 1];
if(rsum[rt << 1 | 1] == m >> 1) rsum[rt] += rsum[rt << 1];
}

void build(int l, int r, int rt) {
lsum[rt] = rsum[rt] = r - l + 1;
if(l == r) return;
int m = l + r >> 1;
build(lson);
build(rson);
}

void update(int o, int v, int l, int r, int rt) {
if(l == r) {
lsum[rt] = rsum[rt] = v;
return;
}
int m = l + r >> 1;
if(o <= m) update(o, v, lson);
else update(o, v, rson);
push_up(rt, r - l + 1);
}

int query(int o, int l, int r, int rt) {
if(l == r) return 0;
int m = l + r >> 1;
if(o >= m - rsum[rt << 1] + 1 && o <= m + lsum[rt << 1 | 1])
return rsum[rt << 1] + lsum[rt << 1 | 1];
if(o <= m) return query(o, lson);
else return query(o, rson);
}

int main() {
#ifdef LOCAL
freopen("in.txt", "r", stdin);
//  freopen("out.txt","w",stdout);
#endif
ios_base::sync_with_stdio(0);

while(scanf("%d%d", &n, &q) == 2) {
build(root);
top = 0;
while(q--) {
char op[2]; int x;
scanf("%s", op);
if(*op == 'R') {
x = stk[--top];
update(x, 1, root);
} else {
scanf("%d", &x);
if(*op == 'D') {
stk[top++] = x;
update(x, 0, root);
} else printf("%d\n", query(x, root));
}
}
}
return 0;
}