线段

题目描述

思路

代码

#include <cstdio>

int n, ans, pre;
struct Node {
	int a, b;
} arr[1000006], tmp;
inline int read() {
	int s = 0, f = 1;
	char ch = getchar();
	while (ch < '0' || ch > '9') {
		if (ch == '-') f = -1;
		ch = getchar();
	}
	while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
	return s * f;
}
void qsort(int L, int R) {
	int l = L, r = R;
	int mid = arr[l + r >> 1].b;
	while (l < r) {
		while (arr[l].b < mid) l++;
		while (arr[r].b > mid) r--;
		if (l <= r) {
			tmp = arr[l];
			arr[l] = arr[r];
			arr[r] = tmp;
			l++, r--;
		}
	}
	if (l < R) qsort(l, R);
	if (L < r) qsort(L, r);
}
int main() {
	n = read();
	for (int i = 1;  i <= n; ++i) arr[i].a = read(), arr[i].b = read();
	qsort(1, n);
	for (int i = 1; i <= n; ++i) {
		if (pre <= arr[i].a) ans++, pre = arr[i].b;
	}
	printf("%d
", ans);
	return 0;
}