[JS][6kyu] Generate All Chess960 Positions

codewars/6kyu/generate-all-chess960-positions/koronya.js

@@ -0,0 +1,65 @@
+// [JS][6kyu] Generate All Chess960 Positions
+// generate-all-chess960-positions
+// https://www.codewars.com/kata/68124e39db8239f29060235b/train/javascript
+
+const uniquePermutations = (s) => {
+  const count = new Map()
+  for (const ch of s) {
+    count.set(ch, (count.get(ch) ?? 0) + 1)
+  }
+  const chars = Array.from(count.keys()).sort()
+  const n = s.length
+  const path = new Array(n)
+  const result = []
+
+  const dfs = (pos) => {
+    if (pos === n) {
+      result.push(path.join(''))
+      return
+    }
+    for (const ch of chars) {
+      const c = count.get(ch)
+      if (!c) {
+        continue
+      }
+      count.set(ch, c - 1)
+      path[pos] = ch
+      dfs(pos + 1)
+      count.set(ch, c)
+    }
+  }
+
+  dfs(0)
+  return result
+}
+
+const ARR = uniquePermutations('bbnnqrkr')
+const VALID_ARR = ARR.filter((item) => {
+  const firstBIndex = item.indexOf('b')
+  const lastBIndex = item.lastIndexOf('b')
+  const firstRIndex = item.indexOf('r')
+  const lastRIndex = item.lastIndexOf('r')
+  const kIndex = item.indexOf('k')
+  if ((lastBIndex - firstBIndex) % 2 === 0) {
+    return false
+  }
+  if (firstRIndex > kIndex || lastRIndex < kIndex) {
+    return false
+  }
+
+  return true
+})
+
+const getChess960Position = (n) => {
+  const str = VALID_ARR[n - 1]
+  const firstRow = str.split('').join(' ')
+  const lastRow = str.toUpperCase().split('').join(' ')
+  const secondRow = 'p p p p p p p p'
+  const emptyRow = '. . . . . . . .'
+  const lastTwoRow = 'P P P P P P P P'
+
+  return [firstRow, secondRow, emptyRow, emptyRow, emptyRow, emptyRow, lastTwoRow, lastRow].join('\n') + '\n'
+}
+
+// getChess960Position(1)
+// getChess960Position(960)