From 1050b4208c48ef399fd84b03dcdc07337627eb0d Mon Sep 17 00:00:00 2001
From: zhangzetao <zhangzetao@wscn.work>
Date: Tue, 10 Nov 2020 17:12:20 +0800
Subject: [PATCH] implement next permutation

---
 permutation.go      | 29 +++++++++++++++++++++++++++++
 permutation_test.go | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 permutation.go
 create mode 100644 permutation_test.go

diff --git a/permutation.go b/permutation.go
new file mode 100644
index 0000000..0b10993
--- /dev/null
+++ b/permutation.go
@@ -0,0 +1,29 @@
+package funk
+
+import "errors"
+
+// NextPermutation Implement next permutation,
+// which rearranges numbers into the lexicographically next greater permutation of numbers.
+func NextPermutation(nums []int) error {
+	n := len(nums)
+	if n == 0 {
+		return errors.New("nums is empty")
+	}
+
+	i := n - 2
+
+	for i >= 0 && nums[i] >= nums[i+1] {
+		i--
+	}
+
+	if i >= 0 {
+		j := n - 1
+		for j >= 0 && nums[i] >= nums[j] {
+			j--
+		}
+		nums[i], nums[j] = nums[j], nums[i]
+	}
+
+	ReverseInt(nums[i+1:])
+	return nil
+}
diff --git a/permutation_test.go b/permutation_test.go
new file mode 100644
index 0000000..99658f3
--- /dev/null
+++ b/permutation_test.go
@@ -0,0 +1,34 @@
+package funk
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestNextPermutation(t *testing.T) {
+	type args struct {
+		nums []int
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+		{
+			name: "case1",
+			args: args{
+				nums: []int{1, 2, 3},
+			},
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := NextPermutation(tt.args.nums); (err != nil) != tt.wantErr {
+				t.Errorf("NextPermutation() error = %v, wantErr %v", err, tt.wantErr)
+			} else {
+				fmt.Println(tt.args.nums)
+			}
+		})
+	}
+}