vault backup: 2022-09-01 13:34:17

.obsidian/appearance.json

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 {
-  "theme": "obsidian",
+  "theme": "moonstone",
   "translucency": true,
   "cssTheme": "Atom",
   "interfaceFontFamily": "IBM Plex Sans",

Leetcode Sort-Colors.md

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+# Leetcode Sort-Colors
+
+#### 2022-09-01 13:24
+
+> ##### Algorithms:
+> #algorithm #two_pointers 
+> ##### Data structures:
+> #DS #array 
+> ##### Difficulty:
+> #coding_problem #difficulty-medium 
+> ##### Additional tags:
+> #leetcode 
+> ##### Revisions:
+> N/A
+
+##### Links:
+- [Link to problem](https://leetcode.com/problems/sort-colors/)
+___
+### Problem
+
+Given an array `nums` with `n` objects colored red, white, or blue, sort them **[in-place](https://en.wikipedia.org/wiki/In-place_algorithm)** so that objects of the same color are adjacent, with the colors in the order red, white, and blue.
+
+We will use the integers `0`, `1`, and `2` to represent the color red, white, and blue, respectively.
+
+You must solve this problem without using the library's sort function.
+
+#### Examples
+
+**Example 1:**
+
+**Input:** nums = [2,0,2,1,1,0]
+**Output:** [0,0,1,1,2,2]
+
+**Example 2:**
+
+**Input:** nums = [2,0,1]
+**Output:** [0,1,2]
+
+#### Constraints
+
+-   `n == nums.length`
+-   `1 <= n <= 300`
+-   `nums[i]` is either `0`, `1`, or `2`.
+
+### Thoughts
+
+> [!summary]
+> This is a variant of double pointer method.
+
+Simple double pointer method, check for cur and pointers to 
+avoid infinite loops.
+
+### Solution
+
+```cpp
+class Solution {
+public:
+  void sortColors(vector<int> &nums) {
+    // Double pointer
+    int lowptr = 0;
+    int highptr = nums.size() - 1;
+    int cur = 0;
+
+    for (int size = nums.size(); cur < size; cur++) {
+      if (nums[cur] == 0 && cur != lowptr) {
+        swap(nums[lowptr++], nums[cur]);
+        cur--;
+      } else if (nums[cur] == 2 && cur < highptr) {
+        swap(nums[highptr--], nums[cur]);
+        cur--;
+      }
+    }
+  }
+};
+```