diff --git a/solution/3400-3499/3470.Permutations IV/solution.go b/solution/3400-3499/3470.Permutations IV/solution.go new file mode 100644 index 0000000000000..3570dd89e3fcb --- /dev/null +++ b/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 +}