Update README.md

Author: riti2409

README.md

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 - Source : https://www.youtube.com/playlist?list=PL_z_8CaSLPWekqhdCPmFohncHwz8TY2Go
 - PDF(of notes) : https://drive.google.com/file/d/1TF2Tm1MCD_3HyrPuL1NhC8qmGV3sOs_u/view?usp=sharing
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+- Note :- The two main approaches to DP problems are memoization(top-down approach) and tabulation (bottom-up approach)
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+While me watching the videos, I saw , many a times he mispelled bottom up as top down . So it might reflect in the notes as well . Please keep this in mind while revising