Workshop › Battleship › Step 24 of 35

A heat map

What we are doing

To shoot smart, the computer imagines every way the ships still afloat could lie on your sea, skipping any that would cross a miss. Each square counts how many of those ways cover it: a heat map. The hottest square is the best guess.

```js
// How many ways could the ships still afloat lie on the sea, given what the computer knows?
function heatMap() {
  const heat = grid(0)
  const afloat = myFleet.filter((s) => !sunk(s)).map((s) => s.cells.length)
  for (const length of afloat) {
    for (let r = 0; r < N; r++) {
      for (let c = 0; c < N; c++) {
        for (const down of [false, true]) {
          const cells = shipCells(r, c, length, down)
          if (cells.some(([cr, cc]) => cr >= N || cc >= N)) continue
          if (cells.some(([cr, cc]) => theirShots[cr][cc] === 'miss')) continue
          for (const [cr, cc] of cells) heat[cr][cc] += 1
        }
      }
    }
  }
  for (let r = 0; r < N; r++) for (let c = 0; c < N; c++) if (theirShots[r][c]) heat[r][c] = 0
  return heat
}
```

What it means

afloat lists the lengths of your ships still afloat.
Four loops try every length, every starting square and both directions.
A placement that leaves the sea or crosses a miss is skipped (continue); every other one adds 1 to its squares.
Squares already shot get 0: no point shooting them again.

Your turn

Under playerShoots, write the comment and heatMap (above computerShoots).

Skills: Loops, Arrays and objects

← You can lose too Shoot the hottest square →

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