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Commit3433f21

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Create 0516-longest-palindromic-subsequence.py
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# Time: O(n^2) Space: O(n^2) - For all three solutions
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classSolution:
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deflongestPalindromeSubseq(self,s:str)->int:
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# Dynamic Programming
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dp= [ [0]* (len(s)+1)foriinrange(len(s)+1)]
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res=0
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foriinrange(len(s)):
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forjinrange(len(s)-1,i-1,-1):
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ifs[i]==s[j]:
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dp[i][j]=1ifi==jelse2
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ifi-1>=0:
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dp[i][j]+=dp[i-1][j+1]
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else:
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dp[i][j]=dp[i][j+1]
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ifi-1>=0:
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dp[i][j]=max(dp[i][j],dp[i-1][j])
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res=max(res,dp[i][j])
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returnres
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# Memoization
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cache= {}
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defdfs(i,j):
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ifi<0orj==len(s):
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return0
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if (i,j)incache:
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returncache[(i,j)]
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ifs[i]==s[j]:
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length=1ifi==jelse2
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cache[(i,j)]=length+dfs(i-1,j+1)
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else:
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cache[(i,j)]=max(dfs(i-1,j),dfs(i,j+1))
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returncache[(i,j)]
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foriinrange(len(s)):
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dfs(i,i)# odd length
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dfs(i,i+1)# even length
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returnmax(cache.values())
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# LCS Solution
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classSolution:
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deflongestPalindromeSubseq(self,s:str)->int:
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returnself.longestCommonSubsequence(s,s[::-1])
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deflongestCommonSubsequence(self,s1:str,s2:str)->int:
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N,M=len(s1),len(s2)
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dp= [[0]* (M+1)for_inrange(N+1)]
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foriinrange(N):
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forjinrange(M):
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ifs1[i]==s2[j]:
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dp[i+1][j+1]=1+dp[i][j]
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else:
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dp[i+1][j+1]=max(dp[i][j+1],dp[i+1][j])
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returndp[N][M]

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