USACO1.2.1 Milking Cows (milk2)

按时刻排序，如果是开始则该点的stat记为+1,结束则记为-1。

记录一个cur值，从左到右扫一遍，每次cur+=现在时刻的stat。如果cur从0变为1,说明进入了有人挤奶段，如果cur从1变为0,说明进入了无人挤奶段。然后再统计最大值。

/*
ID:shijiey1
PROG:milk2
LANG:C++
*/
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

struct Node {
int tim;
int stat;
bool operator < (const Node &n) const {
if (tim != n.tim) return tim < n.tim;
return stat > n.stat;
}
};

int n;
Node arr[12000];
int main() {
freopen("milk2.in", "r", stdin);
freopen("milk2.out", "w", stdout);
scanf("%d", &n);
Node temp;
int a, b;
for (int i = 0; i < n; i++) {
scanf("%d %d", &a, &b);
temp.tim = a;
temp.stat = 1;
arr[i << 1] = temp;
temp.tim = b;
temp.stat = -1;
arr[(i << 1) + 1] = temp;
}
int len = n << 1;
sort(arr, arr + len);
bool on = false;
int busyStart = arr[0].tim;
int freeStart = arr[0].tim;
int busyTime = 0;
int freeTime = 0;
int cur = 0;
bool flag = false;
for (int i = 0; i < len; i++) {
cur += arr[i].stat;
if (!flag) {
freeTime = max(freeTime, arr[i].tim - freeStart);
busyStart = arr[i].tim;
flag = true;
}
if (!cur) {
freeStart = arr[i].tim;
busyTime = max(busyTime, arr[i].tim - busyStart);
flag = false;
}

}
printf("%d %d\n", busyTime, freeTime);
return 0;
}