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poj 1201(查分约束之spfa)
Intervals
Time Limit: 2000MS | Memory Limit: 65536K | |
Total Submissions: 21758 | Accepted: 8191 |
Description
You are given n closed, integer intervals [ai, bi] and n integers c1, ..., cn.
Write a program that:
reads the number of intervals, their end points and integers c1, ..., cn from the standard input,
computes the minimal size of a set Z of integers which has at least ci common elements with interval [ai, bi], for each i=1,2,...,n,
writes the answer to the standard output.
Write a program that:
reads the number of intervals, their end points and integers c1, ..., cn from the standard input,
computes the minimal size of a set Z of integers which has at least ci common elements with interval [ai, bi], for each i=1,2,...,n,
writes the answer to the standard output.
Input
The first line of the input contains an integer n (1 <= n <= 50000) -- the number of intervals. The following n lines describe the intervals. The (i+1)-th line of the input contains three integers ai, bi and ci separated by single spaces and such that 0 <= ai <= bi <= 50000 and 1 <= ci <= bi - ai+1.
Output
The output contains exactly one integer equal to the minimal size of set Z sharing at least ci elements with interval [ai, bi], for each i=1,2,...,n.
Sample Input
5 3 7 3 8 10 3 6 8 1 1 3 1 10 11 1
Sample Output
6
Source
Southwestern Europe 2002
AC代码:
#include<cstring> #include<iostream> #include<stdio.h> #include<stack> using namespace std; struct Node{ int v,w; int next; }Edge[150010]; int n,k; int mx,mn; int head[50005]; int spfa(){ stack <int> st; int vis[50005],dis[50005]; for(int i=mn;i<=mx;i++){ vis[i]=0; dis[i]=-999999; } dis[mn]=0; st.push(mn); while(!st.empty()){ int u=st.top(); st.pop(); vis[u]=0; for(int i=head[u];i;i=Edge[i].next){ int v=Edge[i].v; if(dis[v]<dis[u]+Edge[i].w){ dis[v]=dis[u]+Edge[i].w; if(!vis[v]){ st.push(v); vis[v]=1; } } } } return dis[mx]; } int main(){ while(scanf("%d",&n)!=EOF){ memset(head,0,sizeof(head)); mn=999999; mx=0; k=0; while(n--){ int x,y,s; scanf("%d%d%d",&x,&y,&s); y++; mn=min(x,mn); mx=max(y,mx); k++; Edge[k].v=y; Edge[k].w=s; Edge[k].next=head[x]; head[x]=k; } for(int i=mn;i<mx;i++){ k++; Edge[k].v=i+1; Edge[k].w=0; Edge[k].next=head[i]; head[i]=k; k++; Edge[k].v=i; Edge[k].w=-1; Edge[k].next=head[i+1]; head[i+1]=k; } printf("%d\n",spfa()); } return 0; }
poj 1201(查分约束之spfa)
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