2.19杂

今天晚一做完物理之后冲机房，然后电脑寄了上不了网，换了一台上不了qq，最后换到了刑天遗留下来的电脑（刑天已经离开了我们……

电脑似乎刷过机，很干净……

去洛谷写了道小红题，一直TLE，然后发现快读写错了……

inline int read() {
    int x = 0, f = 1; char c = getchar();
    while (c < '0' || c > '9') { if (c == '-') f = -1; char c = getchar(); }
    while (c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}

昨天用了一天了没发现，我谔谔

写了个数据结构优化DP，写了依托答辩……调了许久

#include <bits/stdc++.h>
#define int long long
const int N = 250005;
const int M = 1000005;
const int INF = 0x3f3f3f3f3f3f3f3f;
using namespace std;
inline int read() {
    int x = 0, f = 1; char c = getchar();
    while (c < '0' || c > '9') { if (c == '-') f = -1; c = getchar(); }
    while (c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}
int n, T;
struct cow {
	int st, ed;
	bool operator< (const cow &y) const  {
		return ed < y.ed || (ed == y.ed && st < y.st);
	}
}a[N];
struct node {
	int l, r, dat;
	#define lc p << 1
	#define rc p << 1 | 1
}t[M << 2];
int f[M];
void pushup(int p) {
	t[p].dat = min(t[lc].dat, t[rc].dat);
}
void build(int p, int l, int r) {
	t[p].l = l, t[p].r = r;
	if (l == r) {
		t[p].dat = f[l];
		return;
	}
	int mid = l + r >> 1;
	build(lc, l, mid);
	build(rc, mid + 1, r);
	pushup(p);
}
void modify(int p, int x, int v) {
	if (t[p].l == t[p].r) {
		t[p].dat = v;
		return;
	}
	int mid = t[p].l + t[p].r >> 1;
    if(x <= mid) modify(lc, x, v);
    else modify(rc, x, v);
    pushup(p);
}
int query(int p, int l, int r) {
	if(t[p].l >= l && t[p].r <= r) return t[p].dat;

    int mid = t[p].l + t[p].r >> 1;
    int res = INF;
    if(l <= mid) res = min(res, query(lc, l, r));
    if(r > mid) res = min(res, query(rc, l, r));
    return res;
}
signed main() {
	n = read(), T = read();
	for (int i = 1; i <= n; i++) {
		a[i].st = read(), a[i].ed = read();
		a[i].st = max(a[i].st, 1ll);
		a[i].ed = min(a[i].ed, T);
	}
		
	sort(a + 1, a + n + 1);
	memset(f, 0x3f, sizeof(f));
	f[0] = 0;
	build(1, 0, T);
	for (int i = 1; i <= n; i++) {
		int l = a[i].st, r = a[i].ed;
		if (l > r) continue;
		int tmp = query(1, l - 1, r);
		f[r] = min(f[r], tmp + 1);
		modify(1, r, f[r]);
	}
	cout << (f[T] == INF ? -1 : f[T]);
}