Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    long[] h = new long[n];
    for(int i = 0; i < n; i++) {
      h[i] = sc.nextLong();
    }
    System.out.println(func(h));
  }

  public static long func(long[] h) {
    long m = Long.MAX_VALUE;
    for(int i = 0; i < h.length; i++) {
      if(m > h[i]) m = h[i];
    }
    ArrayList<Integer> list = new ArrayList<Integer>();
    for(int i = 0; i < h.length; i++) {
      if(h[i] == m) list.add(i);
    }
    long ret = m;
    int k1 = 0;
    int k2 = list.get(0) - 1;
    if(k2 >= k1) {
      long[] s = new long[k2 + 1];
      for(int i = 0; i <= k2; i++) {
        s[i] = h[i] - m;
      }
      ret += func(s);
    }
    for(int i = 0; i < list.size(); i++) {
      int t1 = list.get(i) + 1;
      int t2 = 0;
      if(i < list.size() - 1) {
        t2 = list.get(i + 1) - 1;
      } else {
        t2 = h.length - 1;
      }
      if(t2 >= t1) {
        long[] s = new long[t2 - t1 + 1];
        for(int j = 0; j < (t2 - t1 + 1); j++) {
          s[j] = h[t1 + j] - m;
        }
        ret += func(s);
      }
    }
    return ret;
  }
}