unique paths

Author: fishercoder1534

Common/src/utils/CommonUtils.java

@@ -112,5 +112,16 @@ public static void printList(final ListNode head) {
 		}
 		System.out.println();
 	}
+	
+	public static void printMatrix(int[][] matrix) {
+        System.out.println("Matrix is: ");
+        for(int i = 0; i < matrix.length; i++){
+            for(int j = 0; j < matrix[0].length; j++){
+                System.out.print(matrix[i][j] + "\t");
+            }
+            System.out.println();
+        }
+        System.out.println("----------------------------------------------------");
+    }
 
 }

MEDIUM/src/medium/UniquePaths.java

@@ -0,0 +1,40 @@
+package medium;
+
+import utils.CommonUtils;
+
+/**Leetcode 62. Unique Paths  
+
+A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).
+
+The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).
+
+How many possible unique paths are there?*/
+public class UniquePaths {
+    
+    /**Another typical DP question, use a 2d array:
+     * the first row and the first column need to be initialized to be 1 since there's only one way to reach every
+     * position in the first row and the first column: either from left or top.*/
+    public int uniquePaths(int m, int n) {
+        int[][] dp = new int[m][n];
+        for(int i = 0; i < m; i++) dp[i][0] = 1;
+        for(int i = 0; i < n; i++) dp[0][i] = 1;
+        
+        for(int i = 1; i < m; i++){
+            for(int j = 1; j < n; j++){
+                int ways = 0;
+                if(i-1 >= 0) ways += dp[i-1][j];
+                if(j-1 >= 0) ways += dp[i][j-1];
+                dp[i][j] = ways;
+            }
+        }
+        CommonUtils.printMatrix(dp);
+        return dp[m-1][n-1];
+    }
+    
+    public static void main(String...strings){
+        UniquePaths test = new UniquePaths();
+        int m = 1;
+        int n = 2;
+        System.out.println(test.uniquePaths(m, n));
+    }
+}