two pointers
Easy
| Number | Note | Times |
|---|---|---|
| 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 | Times |
|---|---|---|
| 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 | Times |
|---|---|---|
| 42. Trapping Rain Water |