Number of Islands question in C++ language. Pull Request for Issue #77 (#188)

* added number of islands question

* Update number-of-islands.cpp

* Update README.md

* Update README.md

* Update README.md

Author: Shrimadh

C++/number-of-islands.cpp

@@ -0,0 +1,49 @@
+class Solution {
+public:
+    bool visited[300][300];
+    int r[4] = {-1,0,0,1};
+    int c[4] = {0,-1,1,0};
+    
+    //Checks if the given row and col value are valid and if the cell is visited and if the cell contains '1' or not.
+    bool val(int row,int col,vector<vector<char>>& grid,int M,int N)
+    {
+        return (row<M && col<N && row>=0 && col>=0 && !visited[row][col] && grid[row][col]=='1');
+    }
+    
+    //Dfs function for exploring the surrounding cells
+    void dfs(int i,int j,vector<vector<char>>& grid, int M, int N)
+    {
+        visited[i][j] = true;
+        for(int a=0;a<4;a++)
+        {
+                int row = i + r[a];
+                int col = j + c[a];
+                if(val(row,col,grid,M,N))
+                {
+                    dfs(row,col,grid,M,N);
+                }
+        }
+    }
+    
+    int numIslands(vector<vector<char>>& grid) {
+        int m = grid.size();
+        int n = grid[0].size();
+        memset(visited,0,sizeof(visited));
+        int island_count = 0;
+        for(int i=0;i<m;i++)
+        {
+            for(int j=0;j<n;j++)
+            {
+                if(!visited[i][j] && grid[i][j]=='1')
+                {
+                    dfs(i,j,grid,m,n);
+                    island_count++; // Island count is incremented when there is a cell that has not been visited and contains a '1'.
+                    //Dfs function marks the other connected '1's in the visited matrix.
+                }
+            }
+        }
+        return island_count;
+    }
+};
+/* Time complexity : O(m x n) as each cell is accessed one time.
+   Space complexity : O(m x n) as the visited matrix contains m x n elements.*/

README.md

@@ -347,9 +347,9 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 112  | [Path Sum](https://leetcode.com/problems/path-sum/)                                                        | [Java](./Java/path-sum.java)                       | _O(n)_      | _O(n)_      | Easy       | DFS |      |
 | 110  | [Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)                                | [Java](./Java/Balanced-Binary-Tree.java)           | _O(n)_      | _O(n)_      | Easy       | DFS |      |
 | 1376 | [ Time Needed to Inform All Employees](https://leetcode.com/problems/time-needed-to-inform-all-employees/) | [C++](./C++/Cherry-Pickup-II.cpp)                  | _O(n)_      | _O(n)_      | Medium     | DFS |      |
+| 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/)                                       | [C++](./C++/number-of-islands.cpp)                  | _O(m * n)_ | _O(m * n)_ | Medium     | DFS |      |
 
-|<br/>
-
+<br/>
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@@ -500,6 +500,7 @@ DISCLAIMER: This above mentioned resources have affiliate links, which means if
 | [Sachin_Upadhyay](https://github.com/sachsbu) <br> <img src="https://avatars.githubusercontent.com/u/24941685?v=4" width="100" height="100">                                                                   | India          | Java                  |  [GitHub](https://github.com/sachsbu)                                                                        |
 | [Amisha Sahu](https://github.com/Amisha328) <br> <img src = "https://avatars.githubusercontent.com/u/58816552?v=4" width="100" height="100"> | India | C++ | [CodeChef](https://www.codechef.com/users/amisha328)<br/>[LeetCode](https://leetcode.com/Mishi328/)<br/>[HackerRank](https://www.hackerrank.com/amishasahu328)
 <br/>
+| [Shrimadh V Rao](https://github.com/Shrimadh) <br> <img src="https://avatars.githubusercontent.com/u/64469917?v=4" width="100" height="100">                                                                   | India          | C++                  |  [GitHub](https://github.com/Shrimadh)
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