feat: add go solution to lc problem: No.0031 (doocs#829)

* feat: add go solution to lc problem: No.0202

* feat: add go solution to lc problem: No.0031

Author: Yeqi Tao

.gitignore

@@ -9,4 +9,5 @@
 /lcof/lcof.json
 /lcof/lcof_list.json
 /lcci/lcci.json
-/solution/__pycache__
+/solution/__pycache__
+*.iml

solution/0000-0099/0031.Next Permutation/Solution.go

@@ -0,0 +1,31 @@
+type sortInt []int
+
+func (s sortInt) Len() int {
+	return len(s)
+}
+
+func (s sortInt) Less(i, j int) bool{
+	return s[i] > s[j]
+}
+
+func (s sortInt) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
+func nextPermutation(nums []int)  {
+	newNums := sortInt(nums)
+	if sort.IsSorted(newNums) {
+		n := sort.Reverse(newNums)
+		sort.Sort(n)
+		return
+	}
+	for i := len(nums) -2 ; i >= 0 ; i-- {
+		for j := len(nums) - 1 ; j > i ; j-- {
+			if nums[i] < nums[j] {
+				nums[i],nums[j] = nums[j], nums[i]
+				sort.Sort(sort.Reverse(newNums[i+1:]))
+				return
+			}
+		}
+	}
+}