Problem 56

README.md

@@ -43,7 +43,7 @@ As I work through this list I figure I would make a GitHub repo with my solution
 32. [Clone Graph #133](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/clone-graph-133.md)
 33. Evaluate Reverse Polish Notation #150
 34. Course Schedule #207
-35. Implement Trie (Prefix Tree) #208
+35. **Implement Trie (Prefix Tree) #208**
 36. Coin Change #322
 37. Product of Array Except Self #238
 38. Min Stack #155
@@ -53,7 +53,7 @@ As I work through this list I figure I would make a GitHub repo with my solution
 42. Search in Rotated Sorted Array #33
 43. Combination Sum #39
 44. Permutations #46
-45. Merge Intervals #56
+45. [Merge Intervals #56](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/merge-intervals-56.md)
 46. Lowest Common Ancestor of a Binary Tree #236
 47. Time Based Key-Value Store #981
 48. Accounts Merge #721
@@ -73,7 +73,7 @@ As I work through this list I figure I would make a GitHub repo with my solution
 62. Find All Anagrams in a String #438
 63. Minimum Height Trees #310
 64. Task Scheduler #621
-65. LRU Cache #146
+65. **LRU Cache #146**
 66. Kth Smallest Element in a BST #230
 
 ### Hard
@@ -85,7 +85,7 @@ As I work through this list I figure I would make a GitHub repo with my solution
 71. Word Ladder #127
 72. Basic Calculator #224
 73. Maximum Profit in Job Scheduling #1235
-74. Merge k Sorted Lists #23
+74. **Merge k Sorted Lists #23**
 75. Largest Rectangle in Histogram #84
 
 ## Data Structures
@@ -105,6 +105,7 @@ In order to practice with similar data structures I'll be placing each problem i
 - [Insert Interval #57](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/insert-interval-57.md)
 - [01 Matrix #542](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/01-matrix-542.md)
 - [3Sum #15](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/3Sum-15.md)
+- [Merge Intervals #56](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/merge-intervals-56.md)
 
 ### Queue
 

medium/merge-intervals-56.md

@@ -0,0 +1,71 @@
+# Merge Intervals
+
+Page on leetcode: https://leetcode.com/problems/merge-intervals/
+
+## Problem Statement
+
+Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.
+
+### Constraints
+
+- 1 <= intervals.length <= 104
+- intervals[i].length == 2
+- 0 <= starti <= endi <= 104
+
+### Example
+
+```
+Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
+Output: [[1,6],[8,10],[15,18]]
+Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6].
+```
+
+```
+Input: intervals = [[1,4],[4,5]]
+Output: [[1,5]]
+Explanation: Intervals [1,4] and [4,5] are considered overlapping.
+```
+
+## Solution
+
+- Is intervals always sorted? We will assume yes for now
+
+### Pseudocode
+
+1. Create empty array result
+2. Create curInterval and set to intervals[0]
+3. Iterate thru intervals
+4. ith interval [0] is less than or equal currInterval[1], set curr[0] to min of ith and curr and set curr[1] to max of ith and curr.
+5. Else push curr to result
+6. Set curr equal to ith
+7. Push curr to result
+8. Return result
+
+### Initial Solution
+
+This solution has a time complexity of O(nlogn) due to sorting and a space complexity of O(n) due returning a result array. You can see an explanation of the approach to this problem here: https://www.youtube.com/watch?v=44H3cEC2fFM
+
+```javascript
+const merge = function (intervals) {
+  // In order for below to work need a sorted array. Sort lowest to highest by the 0-index of the interval
+  intervals.sort((a, b) => a[0] - b[0]);
+
+  const result = [];
+  let curr = intervals[0];
+
+  for (let i = 1; i < intervals.length; i++) {
+    if (intervals[i][0] <= curr[1]) {
+      // If there is overlap, update current interval to span the overlapping intervals
+      curr[0] = Math.min(curr[0], intervals[i][0]);
+      curr[1] = Math.max(curr[1], intervals[i][1]);
+    } else {
+      // If no overlap then add current interval to the result and update current interval to the just checked interval
+      result.push(curr);
+      curr = intervals[i];
+    }
+  }
+  result.push(curr);
+
+  return result;
+};
+```