Create solution.go

Author: samarthswami1016

solution/3400-3499/3470.Permutations IV/solution.go

@@ -0,0 +1,51 @@
+func permute(n int, k int64) []int {
+	var f [105]int64
+	f[0] = 1
+	for i := 1; i <= n; i++ {
+		if f[i-1] >= k {
+			f[i] = k
+		} else {
+			f[i] = f[i-1] * int64((i+1)>>1)
+		}
+	}
+	if n%2 == 0 {
+		f[n] *= 2
+	}
+	if f[n] < k {
+		return []int{}
+	}
+	k--
+	ans := make([]int, n)
+	a := [2][]int{}
+	for i := 0; i < n; i++ {
+		a[i&1] = append(a[i&1], i)
+	}
+
+	if n%2 == 1 {
+		ans[0] = int(k/f[n-1]) * 2
+		k -= int64(ans[0]/2) * f[n-1]
+	} else {
+		ans[0] = int(k / f[n-1])
+		k -= int64(ans[0]) * f[n-1]
+	}
+
+	index := sort.SearchInts(a[ans[0]&1], ans[0])
+	a[ans[0]&1] = append(a[ans[0]&1][:index], a[ans[0]&1][index+1:]...)
+
+	for i := 1; i < n; i++ {
+		if n%2 == 1 {
+			ans[i] = a[i&1][k/f[n-i-1]]
+		} else {
+			ans[i] = a[(ans[0]^i)&1][k/f[n-i-1]]
+		}
+		k %= f[n-i-1]
+
+		index = sort.SearchInts(a[ans[i]&1], ans[i])
+		a[ans[i]&1] = append(a[ans[i]&1][:index], a[ans[i]&1][index+1:]...)
+	}
+
+	for i := 0; i < n; i++ {
+		ans[i]++
+	}
+	return ans
+}