study-tutorials
diff --git a/‎526. Beautiful Arrangement.js‎
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+/**
+ * @param {number} n
+ * @return {number}
+ */
+ function countArrangement(N) {
+  let count = 0;
+  const used = [];
+  dfs(1);
+  return count;
+  
+  function dfs(idx) {
+    if (idx > N) {
+      count++;
+      return;
+    }
+    
+    for (let i = 1; i <= N; i++) {
+      if (used[i]) continue;
+      if (i%idx !== 0 && idx%i !== 0) continue;
+      used[i] = true;
+      dfs(idx+1);
+      used[i] = false;
+    }
+  }
+}
+
+// var countArrangement = function(n) {
+//   if(n<=0) return 0
+//   const perms = permutations(n)
+//   let count = 0
+//   for(let perm of perms) {
+//     let valid = true
+//     for(let i=0; i<perm.length; i++) {
+//       if(perm[i]%(i+1)===0 || (i+1)%perm[i]===0)
+//         continue
+//       else {
+//         valid = false
+//         break
+//       }
+//     }
+//     if(valid) count++
+//   }
+//   return count
+// };
+
+// function permutations(n, way=[], result=[]) {
+//   if(way.length===n) {
+//     result.push([...way])
+//     return
+//   }
+//   for(let i=0; i<n; i++) {
+//     if(!way.includes(i+1)) {
+//       way.push(i+1)
+//       permutations(n, way, result)
+//       way.pop()
+//     }
+//   }
+//   return result
+// }