two pointers
Easy
| Number | Note |
|---|---|
| 26. Remove Duplicates from Sorted Array | starting from k=1 and check curr nums[i] with previous nums[k] |
| 27. Remove Element | nums[count] and nums[i] |
| 88. Merge Sorted Array | add the biggest from last to first, use 3 pointers, edge case is second arr remains |
| 125. Valid Palindrome | |
| 283. Move Zeroes | |
| 344. Reverse String | |
| 680. Valid Palindrome II | |
| 844. Backspace String Compare | |
| 977. Squares of a Sorted Array | |
| 1768. Merge Strings Alternately |
Medium
| Number | Note |
|---|---|
| 11. Container With Most Water | two pointer, left right, check min height, find max space, increase or decrease when which one is smaller |
| 15. 3Sum | sort, fix each + 2 pointer, check two consecutive in fix and check two consecutive in pointer (yes, increase left) |
| 16. 3Sum Closest | |
| 18. 4Sum | |
| 167. Two Sum II - Input Array Is Sorted | |
| 189. Rotate Array | |
| 881. Boats to Save People |
Hard
| Number | Note |
|---|---|
| 42. Trapping Rain Water |