Castle Builder

function castleBuilder(heights) {
  if (heights.length < 2) {
    // not enough blocks to build a castle
    return 0;
  }

  let castleCount = 1; // start with 1 castle for the first block
  let direction = ""; // direction of the current slope
  let slopeStart = 0; // index of the start of the current slope

  for (let i = 1; i < heights.length; i++) {
    if (heights[i] > heights[i - 1]) {
      // going up
      if (direction === "down") {
        // end of a valley
        castleCount++;
      }
      direction = "up";
    } else if (heights[i] < heights[i - 1]) {
      // going down
      if (direction === "up" || direction === "") {
        // end of a hill
        castleCount++;
      }
      direction = "down";
    }
    // else, flat land, do nothing

    // update the start of the current slope
    if (direction === "up" || direction === "down" || i === heights.length - 1) {
      slopeStart = i;
    }
  }

  return castleCount;
}

// Test case:
const land0 = [3, -1, -5, -5, 2, 4, 7, 5, 1, 1, 1, 4];
console.log(castleBuilder(land0)); // Output: 5

// Test case 1: flat land
const land1 = [1, 1, 1, 1, 1];
console.log(castleBuilder(land1)); // Output: 0 (no hills or valleys)

// Test case 2: complete hill and valley
const land2 = [1, 2, 3, 4, 3, 2, 1];
console.log(castleBuilder(land2)); // Output: 2 (one hill and one valley)

// Test case 3: incomplete hill and valley at the beginning and end
const land3 = [3, 2, 3, 1, 2, 3, 4];
console.log(castleBuilder(land3)); // Output: 2 (one hill and one valley)

// Test case 4: multiple hills and valleys
const land4 = [3, -1, -5, -5, 2, 4, 7, 5, 1, 1, 1, 4];
console.log(castleBuilder(land4)); // Output: 6 (three hills and three valleys)

// Test case 5: two-block land
const land5 = [1, 2];
console.log(castleBuilder(land5)); // Output: 1 (one hill)

// Test case 6: one-block land
const land6 = [1];
console.log(castleBuilder(land6)); // Output: 0 (not enough blocks to build a castle)