bzoj 3410 [Usaco2009 Dec]Selfish Grazing 自私的食草者 贪心

题面

题目传送门

解法

特别基础的贪心题

就是问最多能选出多少个区间，使得这些区间两两没有交集

直接按照右端点排序，然后贪心取就可以了

时间复杂度：\(O(n\ log\ n)\)

代码

#include <bits/stdc++.h>
#define N 50010
using namespace std;
template <typename node> void chkmax(node &x, node y) {x = max(x, y);}
template <typename node> void chkmin(node &x, node y) {x = min(x, y);}
template <typename node> void read(node &x) {
	x = 0; int f = 1; char c = getchar();
	while (!isdigit(c)) {if (c == '-') f = -1; c = getchar();}
	while (isdigit(c)) x = x * 10 + c - '0', c = getchar(); x *= f;
}
struct Node {
	int l, r;
	bool operator < (const Node &a) const {
		return r < a.r;
	}
} a[N];
int main() {
	int n; read(n);
	for (int i = 1; i <= n; i++)
		read(a[i].l), read(a[i].r), a[i].r--;
	sort(a + 1, a + n + 1);
	int ans = 0, lr = 0;
	for (int i = 1; i <= n; i++)
		if (a[i].l > lr) ans++, lr = a[i].r;
	cout << ans << "\n";
	return 0;
}