POJ 2528 Mayor's posters?（线段树成段更新+离散化）

ACM

题目地址：POJ 2528 Mayor's posters?

题意： 
在[1,10000000]上贴最多10000个线段，问最后有几个线段能露出来。

分析： 
很明显是线段树的成段更新。 
10000000数据量太大，线段树开不了。所以要离散化。 
不过要注意离散化时的问题。不能吧[1,2][4,5]离散化成[1,2][3,4]，因为如果之前有个[1,5]的，原来可以露出来的[3,3]就被离散化忽略了。 
这里没用map离散化，而是用二分找出下标。

代码：

/**  Author:      illuz <iilluzen[at]gmail.com>*  Blog:        http://blog.csdn.net/hcbbt*  File:        2528.cpp*  Create Date: 2014-08-08 16:18:46*  Descripton:  segment tree*/#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <map>using namespace std;#define repf(i,a,b) for(int i=(a);i<=(b);i++)#define lson(x) ((x) << 1)#define rson(x) ((x) << 1 | 1)typedef long long ll;const int N = 50100;const int ROOT = 1;bool mp[N];int t, n, r[N][2], tmp[N<<1], tcnt, ans, cnt;struct seg {int w;};struct segment_tree {seg node[N << 2];void build(int l, int r, int pos) {if (l == r) {node[pos].w = 0;return;}int m = (l + r) >> 1;build(l, m, lson(pos));build(m + 1, r, rson(pos));}void push(int l, int r, int pos) {seg& fa = node[pos];seg& lhs = node[lson(pos)];seg& rhs = node[rson(pos)];int len = r - l + 1;if (node[pos].w) {lhs.w = rhs.w = fa.w;fa.w = 0;}}// add the point [x,y] with zvoid modify(int l, int r, int pos, int x, int y, ll z) {if (x <= l && r <= y) {node[pos].w = z;return;}push(l, r, pos);int m = (l + r) >> 1;if (x <= m)modify(l, m, lson(pos), x, y, z);if (y > m)modify(m + 1, r, rson(pos), x, y, z);}// query the segment [x, y]void query(int l, int r, int pos) {if (node[pos].w) {if (mp[node[pos].w] == 0)ans++;mp[node[pos].w] = 1;return;}if (l == r) {return;}push(l, r, pos);int m = (l + r) >> 1;query(l, m, lson(pos));query(m + 1, r, rson(pos));}} sgm;int bins(int k) {int l = 0, r = cnt - 1;while (l <= r) {int m = (l + r) >> 1;if (tmp[m] == k)return m;if (tmp[m] < k)l = m + 1;elser = m - 1;}return -1;}int main() {scanf("%d", &t);while (t--) {tcnt = 0;scanf("%d", &n);repf (i, 0, n - 1) {scanf("%d%d", &r[i][0], &r[i][1]);tmp[tcnt++] = r[i][0];tmp[tcnt++] = r[i][1];}sort(tmp, tmp + tcnt);cnt = 1;repf (i, 1, tcnt - 1) {if (tmp[i] != tmp[i - 1])tmp[cnt++] = tmp[i];}for (int i = cnt - 1; i > 0; i--) {if (tmp[i] != tmp[i - 1] + 1)tmp[cnt++] = tmp[i - 1] + 1;}sort(tmp, tmp + cnt);sgm.build(1, cnt, ROOT);repf (i, 0, n - 1) {int lhs = bins(r[i][0]) + 1;int rhs = bins(r[i][1]) + 1;sgm.modify(1, cnt, ROOT, lhs, rhs, i + 1);}ans = 0;memset(mp, 0, sizeof(mp));sgm.query(1, cnt, ROOT);printf("%d\n", ans);}return 0;}