From 1bfd42e702b997caf5563b1823be4067cd6ad0a6 Mon Sep 17 00:00:00 2001
From: Invalided <39646604+Invalided@users.noreply.github.com>
Date: Mon, 1 Aug 2022 12:31:24 +0800
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添加 0031.下一个排列Java版本的优化代码，时间复杂度为O(N)，空间复杂度O(1)
---
 problems/0031.下一个排列.md | 46 ++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/problems/0031.下一个排列.md b/problems/0031.下一个排列.md
index 1a3641b0..ada9deba 100644
--- a/problems/0031.下一个排列.md
+++ b/problems/0031.下一个排列.md
@@ -116,6 +116,48 @@ class Solution {
     }
 }
 ```
+> 优化时间复杂度为O(N)，空间复杂度为O(1)
+```Java
+class Solution {
+    public void nextPermutation(int[] nums) {
+        // 1.从后向前获取逆序区域的前一位
+        int index = findIndex(nums);
+        // 判断数组是否处于最小组合状态
+        if(index != 0){
+            // 2.交换逆序区域刚好大于它的最小数字
+            exchange(nums,index);
+        }
+        // 3.把原来的逆序区转为顺序
+        reverse(nums,index);
+    }
+    
+    public static int findIndex(int [] nums){
+        for(int i = nums.length-1;i>0;i--){
+            if(nums[i]>nums[i-1]){
+                return i;
+            }
+        }
+        return 0;
+    }
+    public static void exchange(int [] nums, int index){
+        int head = nums[index-1];
+        for(int i = nums.length-1;i>0;i--){
+            if(head < nums[i]){
+                nums[index-1] = nums[i];
+                nums[i] = head;
+                break;
+            }
+        }
+    }
+    public static void reverse(int [] nums, int index){
+        for(int i = index,j = nums.length-1;i<j;i++,j--){
+            int temp = nums[i];
+            nums[i] = nums[j];
+            nums[j] = temp;
+        }
+    }   
+}
+```
 
 ## Python
 >直接使用sorted()不符合题意
@@ -164,7 +206,7 @@ class Solution:
             high -= 1
 ```
 >上一版本简化版
-'''python
+```python
 class Solution(object):
     def nextPermutation(self, nums: List[int]) -> None:
         n = len(nums)
@@ -185,7 +227,7 @@ class Solution(object):
             end -= 1
         
         return nums
-'''
+```
 
 ## Go