hihocoder 1079 离散化(线段树+区间离散化)

题意：

区间总长为L，依次给n个子区间，后面的覆盖前面的，求最后没有被完全盖住的子区间个数。

离散化：维护区间端点的相对大小关系，将其map到[1, 2n]的区间上。

注意：map之后得到的是端点，而线段树上的节点是单位长度的区间，所以在update的时候应该 update(l, r-1)。。。

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <queue>
#include <iostream>
#include <algorithm>
#include <map>
#include <set>
using namespace std;

#define rep(i, s, t) for(int (i)=(s);(i)<=(t);++(i))
#define urep(i, s, t) for(int (i)=(s);(i)>=(t);--(i))

typedef long long LL;

const int inf  = 0x7fffffff;
const int Maxn = (int)1e5+10;

int li[Maxn], ri[Maxn];
int vis[Maxn];
int n, L;

const int Maxnode = Maxn<<2;
int color[Maxnode];
#define lson(x) ((x)<<1)
#define rson(x) (((x)<<1)|1)
struct SegmentTree {
int length, qL, qR;
void init(int n) {
length = n;
memset(color, -1, sizeof(color));
}

void query(int L, int R) {
qL = L;
qR = R;
_query(1, 1, length);
}

void _query(int o, int L, int R) {
if (color[o] != -1) {
vis[color[o]] = 1;
} else {
if (L == R) return;
int M = (L+R)>>1;
int lc = lson(o), rc = rson(o);
if (qL <= M)
_query(lc, L, M);
if (qR > M)
_query(rc, M+1, R);
}
}

void Set(int L, int R, int v) {
qL = L;
qR = R;
_set(1, 1, length, v);
}

void _set(int o, int L, int R, int v) {
if (qL <= L && qR >= R) {
color[o] = v;
} else {
pushdown(o, L, R);
int M = (L+R)>>1;
int lc = lson(o), rc = rson(o);
if (qL <= M)
_set(lc, L, M, v);
if (qR > M)
_set(rc, M+1, R, v);
}
}

void pushdown(int o, int L, int R) {
if (color[o] != -1) {
int lc = lson(o), rc = rson(o);
color[lc] = color[rc] = color[o];
color[o] = -1;
}
}
};

SegmentTree tree;

int x[Maxn+5];

int main() {
#ifndef ONLINE_JUDGE
freopen("input.in", "r", stdin);
#endif
while (scanf("%d%*d", &n) != EOF) {
if (n == 0) {cout << 0 << endl;continue;}
int cnt = 0;
rep(i, 1, n) {
scanf("%d%d", li+i, ri+i);
x[cnt++] = li[i];
x[cnt++] = ri[i];
}
sort(x, x+cnt);
cnt = unique(x, x+cnt) - x;
tree.init(cnt);
rep(i, 1, n) {
int a = lower_bound(x, x+cnt, li[i])-x+1, b = lower_bound(x, x+cnt, ri[i])-x;
if (a <= b)
tree.Set(a, b, i);
//cout << "map: " << a << ' ' << b << endl;
}
tree.query(1, cnt);
int ans = 0;
rep(i, 1, n)
if (vis[i]) ++ans;
printf("%d\n", ans);
}

return 0;
}