学步园

题目链接：uva 10587 - Mayor's posters

题目大意：就是有一个长度为n的公告板，每次在区间l，r上贴一张海报，问说最后还能看到几张不同的海报。

解题思路：线段树，区间更新，最后统计一下整段区间有多少种不同的海报。

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;
const int maxn = 20005;

#define lson(x) ((x)<<1)
#define rson(x) (((x)<<1)+1)

struct Node {
    int l, r, v, s;
    void set(int l, int r, int v, int s) {
        this->l = l;
        this->r = r;
        this->v = v;
        this->s = s;
    }
    void maintain() {
        v = 1;
        s = r - l + 1;
    }
}nd[maxn * 4];

int N, L[maxn], R[maxn];
vector<int> vec, g;

void pushup(int u) {
    nd[u].s = nd[lson(u)].s + nd[rson(u)].s;
    nd[u].v = (nd[lson(u)].v == nd[rson(u)].v && nd[lson(u)].v == 1 ? 1 : 0);
}

void pushdown(int u) {
    if (nd[u].v) {
        nd[lson(u)].v = nd[rson(u)].v = 1;
        nd[lson(u)].maintain();
        nd[rson(u)].maintain();
        nd[u].v = 0;
    }
}

void build (int u, int l, int r) {
    nd[u].set(l, r, 0, 0);

    if (l == r)
        return;

    int mid = (l + r) / 2;
    build(lson(u), l, mid);
    build(rson(u), mid + 1, r);
    pushup(u);
}

void init () {
    scanf("%d", &N);

    vec.clear();
    for (int i = 0; i < N; i++) {
        scanf("%d%d", &L[i], &R[i]);
        vec.push_back(L[i]);
        vec.push_back(R[i] + 1);
    }
    sort(vec.begin(), vec.end());

    g.clear();
    g.push_back(vec[0]);
    for (int i = 1; i < vec.size(); i++) {
        if (vec[i] != vec[i-1])
            g.push_back(vec[i]);
    }

    for (int i = 0; i < N; i++) {
        L[i] = lower_bound(g.begin(), g.end(), L[i]) - g.begin();
        R[i] = lower_bound(g.begin(), g.end(), R[i] + 1) - g.begin();
    }

    build(1, 0, g.size());
}

int modify (int u, int l, int r) {
    if (l <= nd[u].l && nd[u].r <= r) {
        int tmp = nd[u].s;
        nd[u].maintain();
        return nd[u].s - tmp;
    }

    pushdown(u);
    int mid = (nd[u].l + nd[u].r) / 2, ret = 0;
    if (l <= mid)
        ret += modify(lson(u), l, r);
    if (r > mid)
        ret += modify(rson(u), l, r);
    pushup(u);
    return ret;
}

int main () {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
        init();

        int ret = 0;
        for (int i = N - 1; i >= 0; i--) {
            if(modify(1, L[i], R[i]-1))
                ret++;
        }
        printf("%d\n", ret);
    }
    return 0;
}