The Berland Armed Forces System consists of n ranks that are numbered using natural numbers from 1 to n, where 1 is the lowest rank and n is the highest rank.
One needs exactly di years to rise from rank i to rank i?+?1. Reaching a certain rank i having not reached all the previous i?-?1 ranks is impossible.
Vasya has just reached a new rank of a, but he dreams of holding the rank of b. Find for how many more years Vasya should serve in the army until he can finally realize his dream.
The first input line contains an integer n (2?≤?n?≤?100). The second line contains n?-?1 integers di (1?≤?di?≤?100). The third input line contains two integers a and b (1?≤?a?<?b?≤?n). The numbers on the lines are space-separated.
Print the single number which is the number of years that Vasya needs to rise from rank a to rank b.
解題思路：就是簡單的求區(qū)間和。
直接開個(gè)和數(shù)組，a[i]代表i之前（包括i）的所有數(shù)的和。查詢時(shí)，直接兩個(gè)和減1下便可。
AC代碼：
程序員人生，我編程，我富裕，記住wfuyu網(wǎng)，php教程，php學(xué)習(xí)，php手冊(cè)，CMS模版制作
聲明：本站大部分內(nèi)容是作者原創(chuàng)，少部分收集于互聯(lián)網(wǎng)供大家一起學(xué)習(xí)，原版權(quán)很多不明，如有侵權(quán)請(qǐng)聯(lián)系本站，謝謝！
粵ICP備14040726號(hào)-1?? 2015-2020 程序員人生 版權(quán)所有
