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 JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict";

function groundGarden(heights) {
  // console.log(`loop: heights=${heights}`);
  let lowestHeight = heights[0];
  let lowestIndexes = [0];

  if (!heights.length) { return 0; }

  for (let i = 1; i < flowerNum; i++) {
    const height = heights[i];
    if (height < lowestHeight) {
      lowestHeight = height;
      lowestIndexes = [i];
    } else if (height === lowestHeight) {
      lowestIndexes.push(i);
    } else {
      // ignore
    }
  }
  // console.log(`lowestIndexes=${lowestIndexes}, lowestHeight=${lowestHeight}`);

  if (lowestIndexes.length === flowerNum) {
    // console.log(`return: ${lowestHeight}`);
    return lowestHeight;
  } else {
    const nextHeights = heights.map((x) => x - lowestHeight);
    const water = lowestHeight;

    let sum = 0;
    let subHeights = [];

    for (let i = 0; i < nextHeights.length; i++) {
      if (nextHeights[i] === 0) {
        if (subHeights.length) {
          sum += groundGarden(subHeights);
          subHeights = [];
        }
        continue;
      }

      subHeights.push(nextHeights[i]);
    }

    if (subHeights.length) {
      sum += groundGarden(subHeights);
    }

    return water + sum;
  }
}

const input = require("fs").readFileSync("/dev/stdin", "utf8").split("\n");

const flowerNum = parseInt(input[0], 10);
const heights = input[1].split(" ").map((x) => parseInt(x));

const ans = groundGarden(heights.slice(0, flowerNum));

console.log(ans);