Leetcode/problem1143.py at master · Yuchen112211/Leetcode · GitHub

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'''
1143. Longest Common Subsequence
Medium

Given two strings text1 and text2, return the length of their longest common subsequence.

A subsequence of a string is a new string generated from the original string with some characters(can be none) deleted without changing the relative order of the remaining characters. (eg, "ace" is a subsequence of "abcde" while "aec" is not). A common subsequence of two strings is a subsequence that is common to both strings.


If there is no common subsequence, return 0.


Example 1:

Input: text1 = "abcde", text2 = "ace"
Output: 3
Explanation: The longest common subsequence is "ace" and its length is 3.

Example 2:

Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.

Example 3:

Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0.

Solution:

Classic DP problem.
If i and j equals, plus 1 to the [i-1][j-1]
If not, find the max of [i-1][j] and [i][j-1].

'''

class Solution(object):
	def longestCommonSubsequence(self, text1, text2):
		"""
		:type text1: str
		:type text2: str
		:rtype: int
		"""
		dp = [[0 for i in xrange(len(text2)+1)] for k in xrange(len(text1)+1)]

		for i in range(len(text1)):
			for j in range(len(text2)):
				if text1[i] == text2[j]:
					dp[i+1][j+1] = dp[i][j] + 1
				else:
					dp[i+1][j+1] = max(dp[i+1][j],dp[i][j+1])
		return dp[-1][-1]


s = Solution()
print s.longestCommonSubsequence("abcde","ab")