New Problem "Number of Islands"

Author: haoel

README.md

@@ -7,6 +7,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|184|[Number of Islands](https://leetcode.com/problems/number-of-islands/)| [C++](./algorithms/numberOfIslands/NumberOfIslands.cpp)|Medium|
 |183|[Binary Tree Right Side View](https://leetcode.com/problems/binary-tree-right-side-view/)| [C++](./algorithms/binaryTreeRightSideView/binaryTreeRightSideView.cpp)|Medium|
 |182|[House Robber](https://leetcode.com/problems/house-robber/)| [C++](./algorithms/houseRobber/houseRobber.cpp)|Easy|
 |181|[Number of 1 Bits](https://oj.leetcode.com/problems/number-of-1-bits/)| [C++](./algorithms/numberOf1Bits/numberOf1Bits.cpp)|Easy|

algorithms/numberOfIslands/NumberOfIslands.cpp

@@ -0,0 +1,97 @@
+// Source : https://leetcode.com/problems/number-of-islands/
+// Author : Hao Chen
+// Date   : 2015-06-08
+
+/********************************************************************************** 
+ * 
+ * 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:
+ * 11110110101100000000
+ * Answer: 1
+ * Example 2:
+ * 11000110000010000011
+ * Answer: 3
+ * 
+ * Credits:Special thanks to @mithmatt for adding this problem and creating all test cases.
+ *               
+ **********************************************************************************/
+
+#include <iostream>
+#include <vector>
+using namespace std;
+
+void mark(vector<vector<char> >& grid, int r, int c){
+    if ( r<0 || r>=grid.size() ||
+            c<0 || c>=grid[0].size() ||
+            grid[r][c] != '1' ) {
+        return;
+    }
+
+    grid[r][c] = 'M';
+
+    //left
+    mark(grid, r, c+1);
+    //right
+    mark(grid, r, c-1);
+    //up
+    mark(grid, r-1, c);
+    //down
+    mark(grid, r+1, c);
+}
+
+int numIslands(vector<vector<char> >& grid) {
+    int result = 0;
+    for (int r=0; r<grid.size(); r++) {
+        for (int c=0; c<grid[r].size(); c++) {
+            if (grid[r][c] == '1') {
+                result++;
+                mark(grid, r, c);
+            }
+        }
+    }
+    return result;
+}
+
+void initGrid( string g[], int len, vector<vector<char> >& grid )
+{
+    for (int i=0; i<len; i++){
+       grid.push_back(vector<char>(g[i].begin(), g[i].end())); 
+    }
+}
+
+int main(void)
+{
+    vector< vector<char> > grid;
+    grid.push_back( vector<char>(1, '1') );
+
+    cout << numIslands(grid) << endl;
+
+
+    grid.clear();
+
+    string g1[] = { "11110",
+                    "11010", 
+                    "11000", 
+                    "00000" };
+
+    initGrid(g1, 4, grid);
+    cout << numIslands(grid) << endl;
+
+
+
+    grid.clear();
+
+    string g2[] = { "11000",
+                    "11000",
+                    "00100",
+                    "00011" };
+
+    initGrid(g2, 4, grid);
+    cout << numIslands(grid) << endl;
+
+
+    return 0;
+}