UVA - 11078 - Open Credit System （高效算法的應用！！）

UVA - 11078

Open Credit System Time Limit: 3000MS Memory Limit: Unknown 64bit IO Format: %lld & %llu

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Description

Problem E
Open Credit System
Input: Standard Input

Output: Standard Output

In an open credit system, the students can choose any course they like, but there is a problem. Some of the students are more senior than other students. The professor of such a course has found quite a number of such students who came from senior classes (as if they came to attend the pre requisite course after passing an advanced course). But he wants to do justice to the new students. So, he is going to take a placement test (basically an IQ test) to assess the level of difference among the students. He wants to know the maximum amount of score that a senior student gets more than any junior student. For example, if a senior student gets 80 and a junior student gets 70, then this amount is 10. Be careful that we don't want the absolute value. Help the professor to figure out a solution.

Input
Input consists of a number of test cases T (less than 20). Each case starts with an integer n which is the number of students in the course. This value can be as large as 100,000 and as low as 2. Next n lines contain n integers where the i'th integer is the score of the i'th student. All these integers have absolute values less than 150000. If i < j, then i'th student is senior to the j'th student.

Output
For each test case, output the desired number in a new line. Follow the format shown in sample input-output section.

Sample Input Output for Sample Input

3
 2
 100
 20
 4
 4
 3
 2
 1 

4 

1 

2 

3 

4 

80
3
-1

---

Problemsetter: Mohammad SajjadHossain

Special Thanks: Shahriar Manzoor

Source

Root :: Prominent Problemsetters :: Mohammad Sajjad Hossain
Root :: Competitive Programming 2: This increases the lower bound of Programming Contests. Again (Steven & Felix Halim) :: Problem Solving Paradigms :: Complete Search :: Iterative (The Easier Ones)
Root :: Competitive Programming 3: The New Lower Bound of Programming Contests (Steven & Felix Halim) :: Problem Solving Paradigms :: Complete Search :: Iterative (One Loop, Linear Scan)
Root :: AOAPC I: Beginning Algorithm Contests -- Training Guide (Rujia Liu) :: Chapter 1. Algorithm Design :: Designing Efficient Algorithms :: Examples

AC代碼：

#include 
#include 
using namespace std;

int a[100005], n;

int main()
{
	int T;
	scanf("%d", &T);
	while(T--)
	{
		scanf("%d", &n);
		for(int i = 0; i < n; i++)	scanf("%d", &a[i]);
		int ans = a[0] - a[1];
		int Max = a[0];			//動態維護i之前的最大值 
		for(int i = 1; i < n; i++)
		{
			ans = max(ans, Max - a[i]);
			Max = max(a[i], Max);
		}
		printf("%d\n", ans);
	}
	return 0;
}