poj2376 Cleaning Shifts【线段树】【DP】

  1 #include <iostream>
  2 #include <set>
  3 #include <cmath>
  4 #include <stdio.h>
  5 #include <cstring>
  6 #include <algorithm>
  7 using namespace std;
  8 typedef long long LL;
  9 #define inf 0x7f7f7f7f
 10 
 11 const int maxn = 25000 + 5;
 12 const int maxtime = 1e6 + 5;
 13 struct node{
 14     int st, ed, cost;
 15 }cow[maxn];
 16 bool cmp(node a, node b)
 17 {
 18     return a.ed < b.ed;
 19 }
 20 LL tree[maxtime << 2];//区间中f[]最小值
 21 int n, L, R;
 22 
 23 void pushup(int rt)
 24 {
 25     tree[rt] = min(tree[rt << 1], tree[rt << 1|1]);
 26 }
 27 
 28 void build(int rt, int l, int r)
 29 {
 30     if(l == r){
 31         tree[maxn] = inf;
 32         return;
 33     }
 34     int mid = (l + r) / 2;
 35     build(rt<<1, l, mid);
 36     build(rt<<1|1, mid + 1, r);
 37     pushup(rt);
 38 }
 39 
 40 void update(int x, LL val, int l, int r, int rt)
 41 {
 42     if(l == r){
 43         tree[rt] = min(tree[rt], val);
 44         return;
 45     }
 46     int m = (l + r) / 2;
 47     if(x <= m){
 48         update(x, val, l, m, rt<<1);
 49     }
 50     else{
 51         update(x, val, m + 1, r, rt<<1|1);
 52     }
 53     pushup(rt);
 54 }
 55 
 56 LL query(int L, int R, int l, int r, int rt)
 57 {
 58     if(L <= l && R >= r){
 59         return tree[rt];
 60     }
 61     int m = (l + r) / 2;
 62     LL ans = inf;
 63     if(L <= m){
 64         ans = min(ans, query(L, R, l, m, rt<< 1));
 65     }
 66     if(R > m){
 67         ans = min(ans, query(L, R, m + 1, r, rt<<1|1));
 68     }
 69     pushup(rt);
 70     return ans;
 71 }
 72 
 73 int main()
 74 {
 75     while(scanf("%d%d", &n, &R) != EOF){
 76         R+=1;
 77         memset(tree, 0x7f, sizeof(tree));
 78         for(int i = 1; i <= n; i++){
 79             scanf("%d%d", &cow[i].st, &cow[i].ed);
 80             cow[i].st+=1;cow[i].ed+=1;
 81             cow[i].cost = 1;
 82         }
 83         sort(cow + 1, cow + 1 + n, cmp);
 84 
 85         build(1, 1, R);
 86 
 87         update(1, 0, 1, R, 1);
 88         //cout<<"yes"<<endl;
 89         //int far = L;
 90         bool flag = true;
 91         for(int i = 1; i <= n; i++){
 92             /*if(cow[i].st > far + 1){
 93                 flag = false;
 94             //    break;
 95             }*/
 96             int a = max(1, cow[i].st - 1);
 97             int b = min(R, cow[i].ed);
 98             //cout<<a<<" "<<b<<endl;
 99             LL f = query(a, b, 1, R, 1);
100             f += cow[i].cost;
101             //cout<<f<<endl;
102             update(b, f, 1, R, 1);
103             //far = max(far, cow[i].ed);
104             //cout<<far<<endl;
105         }
106         //cout<<"yes"<<endl;
107 
108         LL ans = query(R, R, 1, R, 1);
109         if(ans >= inf){
110             printf("-1\n");
111         }
112         else{
113                 printf("%lld\n", ans);
114 
115         //else{
116         //    printf("-1\n");
117         }
118 
119     }
120 
121 }