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Author: devaaravmishra

0063-unique-paths-ii/0063-unique-paths-ii.java

@@ -0,0 +1,36 @@
+class Solution { // DP, TOP-DOWN, TC: O(n+m)
+    private int m = 0, n = 0;
+    
+    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+        this.m = obstacleGrid.length;
+        this.n = obstacleGrid[0].length;
+        
+        int[][] dp =  new int[m+1][n+1];
+        
+        for(int[] arr : dp) {
+            Arrays.fill(arr, -1);
+        }
+        
+        return solve(0, 0, obstacleGrid, dp);
+    }
+    private int solve(int i, int j, int[][] obstacleGrid, int[][] dp) {
+        if(i >= m || j >= n || obstacleGrid[i][j] == 1) // reached out of bounds or encountered an obstacle
+            return 0;
+       
+        if(i == m - 1 && j == n - 1) // it's the bottom-right corner
+            return 1;
+        
+        if(dp[i][j] != -1)
+            return dp[i][j];
+        
+        int result = 0;
+        
+        // Down move
+        result += solve(i+1, j, obstacleGrid, dp);
+        
+        // Right move
+        result += solve(i, j+1, obstacleGrid, dp);
+        
+        return dp[i][j] = result;
+    }
+}