PAT-A-1046 Shortest Distance 【前缀和】
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 N integer 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
一道典型的前缀和的问题,如果存储到相邻两个节点的距离,计算两点之间距离需要遍历相加,这样会超时
从第一个节点开始,每个节点纪录到最前面的距离之和,查询的时候直接相减就好了。

如图所示,如果要计算1-3,顺序dis=data[3-1]-data[1-1],即data[2]-data[0],
反序rdis=data[5]-data[3-1]+data[1-1],即data[5]-data[2]+data[0];
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