P1712 [NOI2016]区间
status

线段树维护单点最大值+队列

注意的一点：在下图时

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105 |   while (res(1) == m && pos <= i) {
    |          ~~~~~~~^~~~

由于满足题目限制条件，所以要更新答案！
否则100pts->60pts

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#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define l(x) t[(x)].l
#define r(x) t[(x)].r
#define tag(x) t[(x)].tag
#define res(x) t[(x)].max
using namespace std;

const int MAXN = 5e6 + 10;

struct Segment {
	int max;
	int l;
	int r;
	int tag;
}t[MAXN << 3];

struct Interval {
	int x, y;
	int l;
	bool operator < (const Interval &p) {
		return l < p.l;
	}
}p[MAXN];

int base[MAXN << 1], n, m, cnt;

void build(int p, int x, int y) {
	l(p) = x, r(p) = y;
	if (x != y) {
		int mid = (x + y) >> 1;
		build(p << 1, x, mid);
		build(p << 1 | 1, mid + 1, y);
	}
}

inline void pushdown(int p) {
	if (l(p) != r(p) && tag(p) != 0) {
		int x = tag(p);
		tag(p << 1) += x;
		res(p << 1) += x;
		tag(p << 1 | 1) += x;
		res(p << 1 | 1) += x;
		tag(p) = 0;
	}
}

void printtree(int p) {
	printf("--%d:[%d,%d]--\n", p, l(p), r(p));
	printf("max=%d\n", res(p));
	printf("tag=%d\n", tag(p));
	if (l(p) != r(p)) {
	printf("ls: %d, rs: %d\n", p << 1, p << 1 | 1);
		printtree(p << 1);
		printtree(p << 1 | 1);
	}
}

void modify(int p, int x, int y, int val) {
	if (x > y) return;
	if (x <= l(p) && r(p) <= y) {
		tag(p) += val;
		res(p) += val;
		return;
	}
	int mid = (l(p) + r(p)) >> 1;
	pushdown(p);
	if (x <= mid) {
		modify(p << 1, x, y, val);
	}
	if (mid < y) {
		modify(p << 1 | 1, x, y, val);
	}
	res(p) = max(res(p << 1), res(p << 1 | 1));
}

int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++) {
		scanf("%d%d", &p[i].x, &p[i].y);
		p[i].l = p[i].y - p[i].x;
		base[++cnt] = p[i].x;
		base[++cnt] = p[i].y;
	}
	sort(base + 1, base + cnt + 1);
	cnt = unique(base + 1, base + cnt + 1) - base - 1;
	for (int i = 1; i <= n; i++) {
		p[i].x = lower_bound(base + 1, base + cnt + 1, p[i].x) - base;
		p[i].y = lower_bound(base + 1, base + cnt + 1, p[i].y) - base;
//		printf("[%d->%d]:%d\n", p[i].x, p[i].y, i);
	}
	sort(p + 1, p + n + 1);
	build(1, 1, cnt);
	int pos = 1, ans = 0x3f3f3f3f;
	for (int i = 1; i <= n; i++) {
//		printf("-------------------------pushin:%d-------------------------\n", i);
//		printf("modify : %d->%d:1\n", p[i].x, p[i].y);
		modify(1, p[i].x, p[i].y, 1);
//		printtree(1);
		if (res(1) == m) {
			ans = min(ans, p[i].l - p[pos].l);
		}
		while (res(1) == m && pos <= i) {
//			printf("---------------------------------pushup:%d--------------------\n", pos);
//			printf("---res=%d,m=%d---\n", res(1), m);
			ans = min(ans, p[i].l - p[pos].l);
			if (pos != 0) {
//				printf("modify : %d->%d:-1\n", p[pos].x, p[pos].y);
				modify(1, p[pos].x, p[pos].y, -1);
//				printtree(1);
			}
			pos++;
		}
	}
	if (ans != 0x3f3f3f3f)
		printf("%d\n", ans);
	else
		puts("-1");
	return 0;
}