[CF从零单排#14]116A - Tram
题目来源:http://codeforces.com/problemset/problem/116/A
Linear Kingdom has exactly one tram line. It has n stops, numbered from 1 to n in the order of tram's movement. At the i-th stop a i passengers exit the tram, while b i passengers enter it. The tram is empty before it arrives at the first stop. Also, when the tram arrives at the last stop, all passengers exit so that it becomes empty.
Your task is to calculate the tram's minimum capacity such that the number of people inside the tram at any time never exceeds this capacity. Note that at each stop all exiting passengers exit before any entering passenger enters the tram.
Input
The first line contains a single number n (2 ≤ n ≤ 1000) — the number of the tram's stops.
Then n lines follow, each contains two integers a i and b i (0 ≤ a i, b i ≤ 1000) — the number of passengers that exits the tram at the i-th stop, and the number of passengers that enter the tram at the i-th stop. The stops are given from the first to the last stop in the order of tram's movement.
The number of people who exit at a given stop does not exceed the total number of people in the tram immediately before it arrives at the stop. More formally, . This particularly means that a 1 = 0.
At the last stop, all the passengers exit the tram and it becomes empty. More formally, .
No passenger will enter the train at the last stop. That is, b n = 0.
Output
Print a single integer denoting the minimum possible capacity of the tram (0 is allowed).
Examples
input
4
0 3
2 5
4 2
4 0
output
6
Note
For the first example, a capacity of 6 is sufficient:
At the first stop, the number of passengers inside the tram before arriving is 0. Then, 3 passengers enter the tram, and the number of passengers inside the tram becomes 3.
At the second stop, 2 passengers exit the tram (1 passenger remains inside). Then, 5 passengers enter the tram. There are 6 passengers inside the tram now.
At the third stop, 4 passengers exit the tram (2 passengers remain inside). Then, 2 passengers enter the tram. There are 4 passengers inside the tram now.
Finally, all the remaining passengers inside the tram exit the tram at the last stop. There are no passenger inside the tram now, which is in line with the constraints.
Since the number of passengers inside the tram never exceeds 6, a capacity of 6 is sufficient. Furthermore it is not possible for the tram to have a capacity less than 6. Hence, 6 is the correct answer.
题目大意:
列车线路上有N个站点,每个站点都有乘客上车和下车,每个乘客都坐一个座位,保证乘客先下后上,保证第一个站点是空车,且只有乘客上车,没有下车,所有数据保证合法,且最后所有乘客下车。问列车最少要有多少个座位。
题目分析:
简单模拟题。只需要知道每个站点上下车后,列车中还有多少人,求列车中人数的最大值即可。
参考代码:
#include <bits/stdc++.h>
using namespace std;
int main(){
int a, b, c, n, ans;
cin >> n;
c = ans = 0;
for(int i=1; i<=n; i++){
cin >> a >> b;
c += b-a;
ans = max(c, ans);
}
cout << ans;
return 0;
}