The task is really simple: given N exits on a highway which forms a simple cycle, you are supposed to tell the shortest distance between any pair of exits.
Input Specification:
Each input file contains one test case. For each case, the first line contains an integer N (in [3,105]), followed by Ninteger distances D1 D2 ⋯ DN, where Di is the distance between the i-th and the (i+1)-st exits, and DN is between the N-th and the 1st exits. All the numbers in a line are separated by a space. The second line gives a positive integer M (≤104), with M lines follow, each contains a pair of exit numbers, provided that the exits are numbered from 1 to N. It is guaranteed that the total round trip distance is no more than 107.
Output Specification:
For each test case, print your results in M lines, each contains the shortest distance between the corresponding given pair of exits.
Sample Input:
5 1 2 4 14 9
3
1 3
2 5
4 1
Sample Output:
3
10
7
分析: 题目意思是给了一个环,已经环的每条边(公路)的长度,现给出起点和终点,求出起点和终点之间的最短路径长度,即求顺时针和逆时针行驶的距离最小值。
先求顺时针的距离,而逆时针距离=sum-顺时针距离;
另外暴力求解测试点3会超时,因为每次遍历数组,最大情况10^5个顶点,若有10^4个查询,则一共10^9,对于100ms的时限不能承受。
可以在输入距离时用dis数组记录从1顺时针出发到各顶点的距离。
/** * Copyright(c) * All rights reserved. * Author : Mered1th * Date : 2019-02-23-19.12.21 * Description : A1046 */ #include<cstdio> #include<cstring> #include<iostream> #include<cmath> #include<algorithm> #include<string> #include<unordered_set> #include<map> #include<vector> #include<set> using namespace std; ; int a[maxn],dis[maxn]; int main(){ #ifdef ONLINE_JUDGE #else freopen("1.txt", "r", stdin); #endif ; scanf("%d",&n); ;i<=n;i++){ scanf("%d",&a[i]); sum+=a[i]; dis[i]=sum; } scanf("%d",&m); ;i<m;i++){ ,ans2=; scanf("%d%d",&st,&ed); if(st>ed) swap(st,ed); ans1=dis[ed-]-dis[st-]; ans2=sum-ans1; printf("%d\n",min(ans1,ans2)); } ; }