# README
2337. Move Pieces to Obtain a String
Solution idea
Two Pointers: one pointer for start, one pointer for target
The mechanism is similar to merge part in merge sort.
Key Observation 1
Ignoring _, the relative position of any L and R must remain through their starting and ending positions.
For example: if starting LRR, then ending must be LRR. It can't be other permutations like RLR or RRL.
Key Observation 2
L can only walk towards left, thus, the starting index must $>$ the ending index. In other words, if the starting index $<$ the ending index, then impossible to move like this.
R can only walk towards right, thus, the starting index must $<$ the ending index. In other words, if the starting index $>$ the ending index, then impossible to move like this.
Simpler Solution
Based on above two key observations, a simpler approach is to do 3 passes on start and target:
1st pass: check relative positions of all L and R
2nd pass: check starting (start) and ending (target) index of each L
3rd pass: check starting (start) and ending (target) index of each R
Time complexity = $O(n)$