Update 60-permutation-sequence.js

Author: everthis

60-permutation-sequence.js

@@ -19,3 +19,37 @@ const getPermutation = function (n, k) {
   }
   return sb
 }
+
+// another
+
+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {string}
+ */
+const getPermutation = function(n, k) {
+  let pos = 0
+  const numbers = []
+  const factorial = Array(n + 1).fill(0)
+  let str = ''
+
+  let sum = 1
+  factorial[0] = 1
+
+  for(let i = 1; i <= n; i++) {
+    sum *= i
+    factorial[i] = sum
+  }
+  for(let i = 1; i <= n; i++) {
+    numbers.push(i)
+  }
+  k--
+  for(let i = 1; i <= n; i++) {
+    const idx = ~~(k / factorial[n - i])
+    str += numbers[idx]
+    numbers.splice(idx, 1)
+    k -= idx * factorial[n - i]
+  }
+
+  return str
+};