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+The STRALGO implements complex algorithms that operate on strings. Right now the
+only algorithm implemented is the LCS algorithm (longest common substring).
+However new algorithms could be implemented in the future. The goal of this
+command is to provide to Redis users algorithms that need fast implementations
+and are normally not provided in the standard library of most programming
+languages.
+
+The first argument of the command selects the algorithm to use, right now the
+argument must be "LCS", since this is the only implemented one.
+
+## LCS algorithm
+
+```
+STRALGO LCS [KEYS ...] [STRINGS ...] [LEN] [IDX] [MINMATCHLEN <len>] [WITHMATCHLEN]
+```
+
+The LCS subcommand implements the longest common subsequence algorithm. Note
+that this is different than the longest common string algorithm, since matching
+characters in the string does not need to be contiguous.
+
+For instance the LCS between "foo" and "fao" is "fo", since scanning the two
+strings from left to right, the longest common set of characters is composed of
+the first "f" and then the "o".
+
+LCS is very useful in order to evaluate how similar two strings are. Strings can
+represent many things. For instance if two strings are DNA sequences, the LCS
+will provide a measure of similarity between the two DNA sequences. If the
+strings represent some text edited by some user, the LCS could represent how
+different the new text is compared to the old one, and so forth.
+
+Note that this algorithm runs in `O(N*M)` time, where N is the length of the
+first string and M is the length of the second string. So either spin a
+different Redis instance in order to run this algorithm, or make sure to run it
+against very small strings.
+
+The basic usage is the following:
+
+```
+> STRALGO LCS STRINGS ohmytext mynewtext
+"mytext"
+```
+
+It is also possible to compute the LCS between the content of two keys:
+
+```
+> MSET key1 ohmytext key2 mynewtext
+OK
+> STRALGO LCS KEYS key1 key2
+"mytext"
+```
+
+Sometimes we need just the length of the match:
+
+```
+> STRALGO LCS STRINGS ohmytext mynewtext LEN
+6
+```
+
+However what is often very useful, is to know the match position in each
+strings:
+
+```
+> STRALGO LCS KEYS key1 key2 IDX
+1) "matches"
+2) 1) 1) 1) (integer) 4
+         2) (integer) 7
+      2) 1) (integer) 5
+         2) (integer) 8
+   2) 1) 1) (integer) 2
+         2) (integer) 3
+      2) 1) (integer) 0
+         2) (integer) 1
+3) "len"
+4) (integer) 6
+```
+
+Matches are produced from the last one to the first one, since this is how the
+algorithm works, and it more efficient to emit things in the same order. The
+above array means that the first match (second element of the array) is between
+positions 2-3 of the first string and 0-1 of the second. Then there is another
+match between 4-7 and 5-8.
+
+To restrict the list of matches to the ones of a given minimal length:
+
+```
+> STRALGO LCS KEYS key1 key2 IDX MINMATCHLEN 4
+1) "matches"
+2) 1) 1) 1) (integer) 4
+         2) (integer) 7
+      2) 1) (integer) 5
+         2) (integer) 8
+3) "len"
+4) (integer) 6
+```
+
+Finally to also have the match len:
+
+```
+> STRALGO LCS KEYS key1 key2 IDX MINMATCHLEN 4 WITHMATCHLEN
+1) "matches"
+2) 1) 1) 1) (integer) 4
+         2) (integer) 7
+      2) 1) (integer) 5
+         2) (integer) 8
+      3) (integer) 4
+3) "len"
+4) (integer) 6
+```
+
+@return
+
+For the LCS algorithm:
+
+- Without modifiers the string representing the longest common substring is
+  returned.
+- When LEN is given the command returns the length of the longest common
+  substring.
+- When IDX is given the command returns an array with the LCS length and all the
+  ranges in both the strings, start and end offset for each string, where there
+  are matches. When WITHMATCHLEN is given each array representing a match will
+  also have the length of the match (see examples).