updated README.md

Author: dampdigits

problem66/README.md

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+# 72. Edit Distance
+
+Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2.
+
+You have the following three operations permitted on a word:
+
+Insert a character
+Delete a character
+Replace a character
+ 
+
+## Example 1:
+
+Input: word1 = "horse", word2 = "ros"
+Output: 3
+Explanation: 
+horse -> rorse (replace 'h' with 'r')
+rorse -> rose (remove 'r')
+rose -> ros (remove 'e')
+
+## Example 2:
+
+Input: word1 = "intention", word2 = "execution"
+Output: 5
+Explanation: 
+intention -> inention (remove 't')
+inention -> enention (replace 'i' with 'e')
+enention -> exention (replace 'n' with 'x')
+exention -> exection (replace 'n' with 'c')
+exection -> execution (insert 'u')
+ 
+
+## Constraints:
+
+0 <= word1.length, word2.length <= 500
+word1 and word2 consist of lowercase English letters