vault backup: 2022-07-10 10:22:17

OJ notes/pages/Leetcode Rotate-Array.md

@@ -3,19 +3,19 @@
 #### 2022-07-10 08:54
 
 > ##### Algorithms:
-> #algorithm #array_in_place_operation
+> #algorithm #array_in_place_operation #reverse_array
 > ##### Data structures:
 > #DS #array 
 > ##### Difficulty:
 > #coding_problem #difficulty-medium 
 > ##### Additional tags:
-> #leetcode 
+> #leetcode #CS_list_need_practicing #CS_list_need_understanding 
 > ##### Revisions:
 > N/A
 
 ##### Related topics:
 ```expander
-tag:#array_in_place_operation
+tag:#array_in_place_operation OR #reverse_array 
 ```
  
  
@@ -56,16 +56,49 @@ rotate 2 steps to the right: [3,99,-1,-100]
 
 #### Method 1: Array In-place operation
 
+This one is hard.
+==#TODO: Revisit this one some other day==
+
+- Reversing a subarray doesn't change the continuity, the neighbors inside the subarray is same.
+- Reversing a subarray changes the edge's neighbors
+
+Suppose a array looks like:
+```
+[1, 2,| 3, 4, 5]
+```
+
+If reverse all two subarrays, the neighbors isn't changed 
+only the orders are changed
+
+```
+[1, 2,| 3, 4, 5]:    5-1-2, 1-2-3, 2-3-4, 4-5-1
+[2, 1,| 5, 4, 3]:    3-2-1, 2-1-5, 5-1-4, 4-3-2
+```
+
+When reversed back, the order is changed back to original, but the two sub-arrays are swapped
+
+```
+[3, 4, 5,| 1, 2]
+```
+
+By doing this, the order in inner-array isn't changed, but the order of all is changed.
+
 #### Method 2: Copy
 
 Watch out for integer overflow.
 
-#### Method 3: CPP's STL
+#### Method 3: CPP's STL sway subarrays
-
 
+Remember to sanitize k, when k > size
 
 ### Solution
 
+Method 1:
+
+```cpp
+
+```
+
 Method 2:
 ```cpp
 class Solution {
@@ -96,3 +129,31 @@ public:
   }
 };
 ```
+
+Method 3:
+```cpp
+class Solution {
+  void swap(vector<int> &nums, int l, int r) {
+    int temp = nums[l];
+    nums[l] = nums[r];
+    nums[r] = temp;
+  }
+
+public:
+  void rotate(vector<int> &nums, int k) {
+    int size = nums.size();
+    if (size <= 1) {
+      return;
+    }
+    // STL
+    k = k % size;
+    k = size - k;
+    while (k < 0) {
+      k += size;
+    }
+
+    nums.insert(nums.end(), nums.begin(), nums.begin() + k);
+    nums.erase(nums.begin(), nums.begin() + k);
+  }
+};
+```