solves unique paths ii

Author: anishLearnsToCode

Diff for: README.md

@@ -60,6 +60,7 @@
 |  59  | [Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii)                                                                                        |                                                                 [![Java](assets/java.png)](src/SpiralMatrixII.java)                                                                  |                                                                                                                                   |
 |  61  | [Rotate List](https://leetcode.com/problems/rotate-list)                                                                                                  |                                                                   [![Java](assets/java.png)](src/RotateList.java)                                                                    |                                                                                                                                   |
 |  62  | [Unique Paths](https://leetcode.com/problems/unique-paths)                                                                                                |                                                                   [![Java](assets/java.png)](src/UniquePaths.java)                                                                   |                                                                                                                                   |
+|  63  | [Unique Paths II](https://leetcode.com/problems/unique-paths-ii)                                                                                          |                                                                  [![Java](assets/java.png)](src/UniquePathII.java)                                                                   |                                                                                                                                   |
 |  66  | [Plus One](https://leetcode.com/problems/plus-one)                                                                                                        |                                           [![Java](assets/java.png)](src/PlusOne.java) [![Python](assets/python.png)](python/plus_one.py)                                            |                                                                                                                                   |
 |  67  | [Add Binary](https://leetcode.com/problems/add-binary)                                                                                                    |                                         [![Java](assets/java.png)](src/AddBinary.java) [![Python](assets/python.png)](python/add_binary.py)                                          |                                                                                                                                   |
 |  69  | [Sqrt(x)](https://leetcode.com/problems/sqrtx)                                                                                                            |                                              [![Java](assets/java.png)](src/Sqrtx.java) [![Python](assets/python.png)](python/sqrt.py)                                               |                                                                                                                                   |

Diff for: src/UniquePathII.java

@@ -0,0 +1,35 @@
+// https://leetcode.com/problems/unique-paths-ii
+// T: O(m * n)
+// S: O(n)
+
+public class UniquePathII {
+    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+        final int rows = obstacleGrid.length, columns = obstacleGrid[0].length;
+        if (obstacleGrid[rows - 1][columns - 1] == 1) return 0;
+        final int[][] memory = getMemoryTable(obstacleGrid);
+
+        int i = 0;
+        for (int row = rows - 2 ; row >= 0; row--, i ^= 1) {
+            memory[i][columns - 1] = memory[i ^ 1][columns - 1] & (obstacleGrid[row][columns - 1] ^ 1);
+            for (int column = columns - 2 ; column >= 0 ; column--) {
+                if (obstacleGrid[row][column] == 1) {
+                    memory[i][column] = 0;
+                } else {
+                  memory[i][column] = memory[i ^ 1][column] + memory[i][column + 1];
+                }
+            }
+        }
+
+        return memory[i ^ 1][0];
+    }
+
+    private int[][] getMemoryTable(int[][] obstacles) {
+        final int rows = obstacles.length, columns = obstacles[0].length;
+        final int[][] memory = new int[2][columns];
+        memory[1][columns - 1] = 1;
+        for (int column = columns - 2 ; column >= 0 ; column--) {
+            memory[1][column] = memory[1][column + 1] & (obstacles[rows - 1][column] ^ 1);
+        }
+        return memory;
+    }
+}