Update README.md

README.md

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-# DFS-2
+# DFS-2
+
+## Problem1 (https://leetcode.com/problems/number-of-islands/)
+Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
+
+Example 1:
+
+Input:
+
+11110
+
+11010
+
+11000
+
+00000
+
+Output: 1
+Example 2:
+
+Input:
+
+11000
+
+11000
+
+00100
+
+00011
+
+Output: 3
+
+## Problem2 (https://leetcode.com/problems/decode-string/)
+Given an encoded string, return its decoded string.
+
+The encoding rule is: k[encoded_string], where the encoded_stringinside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer.
+
+You may assume that the input string is always valid; No extra white spaces, square brackets are well-formed, etc.
+
+Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k. For example, there won't be input like 3a or 2[4].
+
+Examples:
+
+s = "3[a]2[bc]", return "aaabcbc".
+
+s = "3[a2[c]]", return "accaccacc".
+
+s = "2[abc]3[cd]ef", return "abcabccdcdcdef".