add solution of problem 62: unique path

Author: ppulse

UniquePaths62/README.md

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+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?
+
+![thisImg](http://leetcode.com/wp-content/uploads/2014/12/robot_maze.png)
+Above is a 3 x 7 grid. How many possible unique paths are there?
+
+**Note:** *m* and *n* will be at most 100.

UniquePaths62/Solution.java

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+public class Solution {
+    public int uniquePaths(int m, int n) {
+        if (m <= 0 || n <= 0)
+            return -1;
+        
+        int[][] result = new int[m][n];
+        result[0][0] = 1;
+        
+        for (int i = 1; i < m; i++) {
+            result[i][0] = 1;
+        }
+        
+        for (int i = 1; i < n; i++) {
+            result[0][i] = 1;
+        }
+        
+        for (int i = 1; i < m; i++) {
+            for (int j = 1; j < n; j++) {
+                result[i][j] += result[i-1][j] + result[i][j-1];
+            }    
+        }
+        
+        return result[m-1][n-1];
+    }
+}