add solution of problem 63: unique paths II

Author: ppulse

UniquePathsII63/README.md

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+Follow up for "Unique Paths":
+
+Now consider if some obstacles are added to the grids. How many unique paths would there be?
+
+An obstacle and empty space is marked as `1` and `0` respectively in the grid.
+
+For example,
+There is one obstacle in the middle of a 3x3 grid as illustrated below.
+```
+[
+  [0,0,0],
+  [0,1,0],
+  [0,0,0]
+]
+```
+The total number of unique paths is `2`.
+
+**Note:** *m* and *n* will be at most 100.

UniquePathsII63/Solution.java

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+public class Solution {
+    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+        if (obstacleGrid == null || obstacleGrid.length == 0 
+          || obstacleGrid[0].length == 0 || obstacleGrid[0][0] == 1)
+            return 0;
+        
+        int m = obstacleGrid.length;
+        int n = obstacleGrid[0].length;
+        
+        int[][] result = new int[m][n];
+        result[0][0] = 1;
+        
+        for (int i = 1; i < m; i++) {
+            if (obstacleGrid[i][0] == 1)
+                break;
+            
+            result[i][0] = 1;
+        }
+        
+        for (int i = 1; i < n; i++) {
+            if (obstacleGrid[0][i] == 1)
+                break;
+            
+            result[0][i] = 1;
+        }
+        
+        for (int i = 1; i < m; i++) {
+            for (int j = 1; j < n; j++) {
+                if (obstacleGrid[i][j] == 1)
+                    result[i][j] = 0;
+                else
+                    result[i][j] = result[i-1][j] + result[i][j-1];
+            }
+        }
+        
+        return result[m-1][n-1];
+    }
+}