Unique Paths II

Author: mengli

UniquePathsII.java

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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.
+ *
+ */
+public class UniquePathsII {
+	public int uniquePathsWithObstacles(int[][] obstacleGrid) {
+		int m = obstacleGrid.length;
+		if (m == 0)
+			return 0;
+		int n = obstacleGrid[0].length;
+		int[][] map = new int[m][n];
+		map[0][0] = obstacleGrid[0][0] == 1 ? 0 : 1;
+		for (int i = 1; i < m; i++) {
+			map[i][0] = obstacleGrid[i][0] == 1 ? 0 : map[i - 1][0];
+		}
+		for (int j = 1; j < n; j++) {
+			map[0][j] = obstacleGrid[0][j] == 1 ? 0 : map[0][j - 1];
+		}
+		for (int i = 1; i < m; i++) {
+			for (int j = 1; j < n; j++) {
+				map[i][j] = obstacleGrid[i][j] == 1 ? 0 : map[i - 1][j]
+						+ map[i][j - 1];
+			}
+		}
+		return map[m - 1][n - 1];
+	}
+}