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[100010];
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=1, flag=0;
    cin >> n >> t;
    for(int i = 0; i < n; i++){
        cin >> node[i].x >> node[i].y;
    }
    sort(node, node+n, cmp);
    if(node[0].x != 1){
        cout << "-1" << endl;
        return 0;
    }
    else if(node[0].y == t){
        cout << "1" << endl;
        return 0;
    }
    else {
        int end = node[0].y, pre, maxm = node[0].y;
        for(int i = 1; i < n; i++){
            pre = maxm;
            while(i < n&&node[i].x<=end+1){//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=1;
                break;
            }
            else if(pre == maxm){
                break;
            }
            else{
                end = maxm;
                cnt++;
            }
        }
        if(!flag) cout << "-1" << endl;
        else
            cout << cnt << endl;
    }
    return 0;
}