POJ 2528 Mayor's posters（线段树+离散化）

#include <cstdio>
#include <iostream>
#include <string>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <vector>
#include <map>
using namespace std;
#define ll long long

int t, n, ans;
int a[400000+8], pos[100000+8][2];
bool sign[400000+8];

struct edge///离散
{
    int l, r;
}e[400000+8];

struct node
{
    int l, r, num;
}tree[400000+8];

void build(int i, int l, int r)///建树
{
    tree[i].l = l;
    tree[i].r = r;
    tree[i].num = 0;
    if(tree[i].l == tree[i].r)///tree[i].l与l无区别，tree[i].r与r无区别
        return;
    int mid = (tree[i].l + tree[i].r) / 2;///tree[i].l与l无区别，tree[i].r与r无区别
    build(i * 2, l, mid);
    build(i * 2 + 1, mid + 1, r);
}

void push_down(int i)///向下传递num的值
{
    if(tree[i].num != 0)
    {
        tree[i * 2].num = tree[i * 2 + 1].num = tree[i].num;
        tree[i].num = 0;
    }
    return;
}

void pls(int i, int l, int r, int k)///区间修改
{
    if(tree[i].l >= l && tree[i].r <= r)
    {
        tree[i].num = k;
        return;
    }
    push_down(i);
    int mid = (tree[i].l + tree[i].r) / 2;///tree[i].l与l无区别，tree[i].r与r无区别
    if(l <= mid)
        pls(i * 2, l, r, k);
    if(mid < r)
        pls(i * 2 + 1, l, r, k);
}

void search(int i)
{
    if(tree[i].num != 0)///如果那个点不等于0
    {
        if(!sign[tree[i].num])///且这个点的值没数过
        {
            sign[tree[i].num] = 1;///标记他数过了
            ans++;///总数量加
        }
        return;
    }
    search(i * 2);
    search(i * 2 + 1);
}

int main()
{
    for(scanf("%d", &t); t--; )///
    {
        memset(sign, 0, sizeof(sign));
        memset(a, 0, sizeof(a));
        memset(pos, 0, sizeof(pos));
        scanf("%d", &n);
        int id = 1;
        for(int i = 1; i <= n; i++)
        {
            scanf("%d%d", &pos[i][0], &pos[i][1]);
            a[id++] = pos[i][0];
            a[id++] = pos[i][1];
        }
        sort(a + 1, a + id);
        int index = 1;
        for(int i = 2; i < id; i++)
            if(a[i] != a[i-1])
                a[++index] = a[i];///到这里数据就变了，也不知道怎么回事
        ans = 0;
        int r = -1;
        for(int i = 1; i <= n; i++)
        {
            e[i].l = lower_bound(a + 1, a + index + 1, pos[i][0]) - a;
            e[i].r = lower_bound(a + 1, a + index + 1, pos[i][1]) - a;
            r = max(r, e[i].r);///确定区间最长可到达哪里
        }
        build(1, 1, r);
        for(int i = 1; i <= n; i++)
            pls(1, e[i].l, e[i].r, i);
        search(1);
        printf("%d\n", ans);
    }
    return 0;
}