Given two strings, find the longest common subsequence (LCS).

Example

Example 1:
Input: "ABCD" and "EDCA"
Output: 1 Explanation:
LCS is 'A' or 'D' or 'C' Example 2:
Input: "ABCD" and "EACB"
Output: 2 Explanation:
LCS is "AC"
这个题目思路是利用dynamic programming,用二维的,mem[l1 + 1][l2 + 1] # mem[i][j] 去表示s1的前i个characters与s2的前j个characters的LCS的length。
function : mem[i][j] = max(mem[i][j - 1], mem[i - 1][j]) if s1[i - 1] != s2[j - 1]
              max(mem[i][j - 1], mem[i - 1][j], mem[i - 1][j - 1] + 1) if s1[i - 1] == s2[j - 1]
initialize : mem[i][0] = mem[0][j] = 0 Code:
class Solution:
def LCS(self, s1, s2):
l1, l2 = len(s1), len(s2)
mem = [[0] * (l2 + 1) for _ in range(l1 + 1)]
for i in range(1, l1 + 1):
for j in range(1, l2 + 1):
temp = 1 if s1[i - 1] == s2[j - 1] else 0:
mem[i][j] = max(mem[i - 1][j], mem[i][j - 1], mem[i - 1][j - 1] + temp)
return mem[l1][l2]
 

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