battleships.js

/**
 * @param {character[][]} board
 * @return {number}
 */
var countBattleships = function(board) {
  return countBattleshipsRec(board, 0, 0, false)
};

const mem = {}
function countBattleshipsRec(board, x, y, inAShip) {
  let ships = 0;
  if (board[x][y] === "X" && !mem[`${x}-${y}`]) {
    if (!inAShip) {
      ships++
      inAShip = true
      
      for (let i=y; i >= 0; i--) {
        if (board[x][i] === "X") {
          mem[`${x}-${i}`] = true
        }
      }
    }
  } else {
    inAShip = false
  }
  
  if (x + 1 < board.length) {
    ships += countBattleshipsRec(board, x+1, y, inAShip)
  }
  
  if (y + 1 < board[x].length) {
    ships += countBattleshipsRec(board, x, y+1, inAShip)
  }
  
  return ships
}