feat: add cpp solution to lc problem: No.0031 (doocs#783)

No.0031.Next Permutation

Author: Dhoni77

solution/0000-0099/0031.Next Permutation/README.md

@@ -78,10 +78,32 @@
 
 ```
 
-### **...**
-
-```
-
+### **C++**
+
+```cpp
+class Solution {
+public:
+    void nextPermutation(vector<int>& nums) {
+        int i, j;
+        int n = nums.size();
+        for (i = n - 2; i >= 0; i--) {
+            if (nums[i] < nums[i + 1]) {
+                break;
+            }
+        }
+        if (i < 0)
+            reverse(nums.begin(), nums.end());
+        else {
+            for (j = n - 1; j >= 0; j--) {
+                if (nums[i] < nums[j]) {
+                    break;
+                }
+            }
+            swap(nums[i], nums[j]);
+            reverse(nums.begin() + i + 1, nums.end());
+        }
+    }
+};
 ```
 
 <!-- tabs:end -->

solution/0000-0099/0031.Next Permutation/README_EN.md

@@ -68,10 +68,32 @@
 
 ```
 
-### **...**
-
-```
-
+### **C++**
+
+```cpp
+class Solution {
+public:
+    void nextPermutation(vector<int>& nums) {
+        int i, j;
+        int n = nums.size();
+        for (i = n - 2; i >= 0; i--) {
+            if (nums[i] < nums[i + 1]) {
+                break;
+            }
+        }
+        if (i < 0)
+            reverse(nums.begin(), nums.end());
+        else {
+            for (j = n - 1; j >= 0; j--) {
+                if (nums[i] < nums[j]) {
+                    break;
+                }
+            }
+            swap(nums[i], nums[j]);
+            reverse(nums.begin() + i + 1, nums.end());
+        }
+    }
+};
 ```
 
 <!-- tabs:end -->

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

@@ -1,20 +1,23 @@
 class Solution {
 public:
-    void nextPermutation(vector<int> &nums) {
-	    int len = nums.size();
-
-	    if (len == 0)return;
-        int i,j;
-        for(i = len - 2;i>=0;i--){
-            if(nums[i+1] > nums[i]){
-                for(j = len - 1;j>i;j--){
-                    if(nums[j]>nums[i])break;
-                }   
-                swap(nums[i],nums[j]);
-                reverse(nums.begin()+i+1,nums.end());           
-                return;
+    void nextPermutation(vector<int>& nums) {
+        int i, j;
+        int n = nums.size();
+        for (i = n - 2; i >= 0; i--) {
+            if (nums[i] < nums[i + 1]) {
+                break;
             }
         }
-	    reverse(nums.begin(),nums.end());
+        if (i < 0)
+            reverse(nums.begin(), nums.end());
+        else {
+            for (j = n - 1; j >= 0; j--) {
+                if (nums[i] < nums[j]) {
+                    break;
+                }
+            }
+            swap(nums[i], nums[j]);
+            reverse(nums.begin() + i + 1, nums.end());
+        }
     }
 };