poj2376 Cleaning Shifts（区间贪心，理解题意）

https://vjudge.net/problem/POJ-2376

题意理解错了！！真是要仔细看题啊！！

看了poj的discuss才发现，如果前一头牛截止到3，那么下一头牛可以从4开始！！！

 #include<iostream>
 #include<cstdio>
 #include<queue>
 #include<cstring>
 #include<algorithm>
 #include<cmath>
 #include<set>
 #define INF 0x3f3f3f3f
 typedef long long ll;
 using namespace std;
 typedef struct{
     int x, y;
 }Node;
 Node node[];
 bool cmp(const Node a, const Node b)
 {
     if(a.x != b.x)
         return a.x<b.x;
     else
         return a.y>b.y;
 }//起点相同则返回终点大的，否则返回起点小的
 int main()
 {
     int n, t, cnt=, flag=;
     cin >> n >> t;
     for(int i = ; i < n; i++){
         cin >> node[i].x >> node[i].y;
     }
     sort(node, node+n, cmp);
     if(node[].x != ){
         cout << "-1" << endl;
         return ;
     }
     else if(node[].y == t){
         cout << "" << endl;
         return ;
     }
     else {
         int end = node[].y, pre, maxm = node[].y;
         for(int i = ; i < n; i++){
             pre = maxm;
             while(i < n&&node[i].x<=end+){//这里理解错了！！
                 if(maxm < node[i].y){
                     maxm = node[i].y;
                 }
                 i++;
             }
             i--;
             //cout << maxm << endl;
             if(maxm == t){
                 cnt++;
                 flag=;
                 break;
             }
             else if(pre == maxm){
                 break;
             }
             else{
                 end = maxm;
                 cnt++;
             }
         }
         if(!flag) cout << "-1" << endl;
         else
             cout << cnt << endl;
     }
     return ;
 }