unique paths II

fishercoder1534 · fishercoder1534 · commit 8ee888d7d696 · 2016-07-31T11:46:09.000-07:00
diff --git a/MEDIUM/src/medium/UniquePathsII.java b/MEDIUM/src/medium/UniquePathsII.java
@@ -0,0 +1,84 @@
+package medium;
+
+import utils.CommonUtils;
+
+/**63. Unique Paths II  QuestionEditorial Solution  My Submissions
+Total Accepted: 72924
+Total Submissions: 243328
+Difficulty: Medium
+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.*/
+public class UniquePathsII {
+    /**Idea: grid[i][j] has to be set to zero if obstacleGrid[i][j] == 1,
+     * otherwise, we can get dp[i][j] from its top and left dp.*/
+    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+        if(obstacleGrid == null || obstacleGrid.length == 0) return 0;
+        
+        int height = obstacleGrid.length, width = obstacleGrid[0].length;
+        int[][] dp = new int[height][width];
+        dp[0][0] = obstacleGrid[0][0] == 1 ? 0 : 1;
+        for(int i = 1; i < height; i++){
+            dp[i][0] = obstacleGrid[i][0] == 1 ? 0 : dp[i-1][0];
+        }
+        for(int j = 1; j < width; j++){
+            dp[0][j] = obstacleGrid[0][j] == 1 ? 0 : dp[0][j-1];
+        }
+        
+        for(int i = 1; i < height; i++){
+            for(int j = 1; j < width; j++){
+                if(obstacleGrid[i][j] == 1) dp[i][j] = 0;
+                else {
+                    int paths = 0;
+                    if(obstacleGrid[i-1][j] == 0) paths += dp[i-1][j];
+                    if(obstacleGrid[i][j-1] == 0) paths += dp[i][j-1];
+                    dp[i][j] =  paths;
+                }
+            }
+        }
+        CommonUtils.printMatrix(dp);
+        return dp[height-1][width-1];
+    }
+    
+    public static void main(String...strings){
+        UniquePathsII test = new UniquePathsII();
+//        int[][] obstacleGrid = new int[3][3];
+//        obstacleGrid[0][0] = 0;
+//        obstacleGrid[0][1] = 0;
+//        obstacleGrid[0][2] = 0;
+//        obstacleGrid[1][0] = 0;
+//        obstacleGrid[1][1] = 1;
+//        obstacleGrid[1][2] = 0;
+//        obstacleGrid[2][0] = 0;
+//        obstacleGrid[2][1] = 0;
+//        obstacleGrid[2][2] = 0;
+        
+//        int[][] obstacleGrid = new int[1][2];
+//        obstacleGrid[0][0] = 1;
+//        obstacleGrid[0][1] = 0;
+        
+        int[][] obstacleGrid = new int[2][2];
+        obstacleGrid[0][0] = 0;
+        obstacleGrid[0][1] = 0;
+        obstacleGrid[1][0] = 0;
+        obstacleGrid[1][1] = 1;
+        
+        CommonUtils.printMatrix(obstacleGrid);
+        System.out.println(test.uniquePathsWithObstacles(obstacleGrid));
+    }
+
+}
