ALDS1_1_D Maximum Profit

Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency RtRt at a certain time tt (t=0,1,2,...n−1t=0,1,2,...n−1), and reports the maximum value of Rj−RiRj−Ri where j>ij>i .

Input

The first line contains an integer nn. In the following nn lines, RtRt (t=0,1,2,...n−1t=0,1,2,...n−1) are given in order.

Output

Print the maximum value in a line.

Constraints

• 2≤n≤200,0002≤n≤200,000
• 1≤Rt≤1091≤Rt≤109

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

分析：用一个变量记录下最小的那个R,另一个变量记录最大的利润，一次扫描。因为这是有时间顺序的！

#include<iostream>
#include<vector>
using namespace std;

int maxProfit(vector<int>& A, int N){
  int maxProfit = -2000000000;
  int minR = A[0];
  for (int i=1;i<N;i++){
      maxProfit = max(maxProfit, A[i] - minR);
      minR = min(minR, A[i]);
  }
  return maxProfit;
}

int main(){
 int N;
 cin>>N;
 vector<int> A(N);
 for(int i =0; i <N; i++) cin>>A[i];

 int sw = maxProfit(A,N);
 cout<<sw<<endl;
}