Add java solution to LC63

Author: kate-melnykova

LC63-Unique-Paths-II.java

@@ -0,0 +1,61 @@
+/*
+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).
+
+Now consider if some obstacles are added to the grids. How many
+unique paths would there be?
+
+An obstacle and space is marked as 1 and 0 respectively in the grid.
+
+Example 1:
+Input: obstacleGrid = [[0,0,0],[0,1,0],[0,0,0]]
+Output: 2
+Explanation: There is one obstacle in the middle of the 3x3 grid above.
+There are two ways to reach the bottom-right corner:
+1. Right -> Right -> Down -> Down
+2. Down -> Down -> Right -> Right
+
+Example 2:
+Input: obstacleGrid = [[0,1],[0,0]]
+Output: 1
+
+
+Constraints:
+m == obstacleGrid.length
+n == obstacleGrid[i].length
+1 <= m, n <= 100
+obstacleGrid[i][j] is 0 or 1.
+*/
+
+class Solution {
+    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+        int m = obstacleGrid.length;
+        int n = obstacleGrid[0].length;
+        int[] paths = new int[n];
+        if ((obstacleGrid[0][0] == 1) | (obstacleGrid[m-1][n-1] == 1)){
+            return 0;
+        }
+        int i = 0;
+        while ((i < n) && (obstacleGrid[0][i] == 0)){
+            paths[i] = 1;
+            i++;
+        }
+        for (i=1; i < m; i++){
+            if (obstacleGrid[i][0] == 1){
+                paths[0] = 0;
+            }
+            for (int j = 1; j < n; j++){
+                if (obstacleGrid[i][j] == 0){
+                    paths[j] = paths[j] + paths[j-1];
+                } else {
+                    paths[j] = 0;
+                }
+            }
+        }
+        return paths[n-1];
+    }
+}