feat(solutions): add unique_paths_ii

Author: WindomZ

README.md

@@ -24,6 +24,7 @@
 
 | # | Problem | Solution | Difficulty | Single Repetition Duration | LeetCode Run Time |
 | ---: | :----- | :--------: | :----------: | ----------: | ----------: |
+|63|[Unique Paths II][Solutions-63]|[WindomZ][Solutions-63-Go]|Medium|[36.3 ns/op/5 test cases][Solutions-63-Test]|? ms|
 |62|[Unique Paths][Solutions-62]|[WindomZ][Solutions-62-Go]|Medium|[9.39 ns/op/10 test cases][Solutions-62-Test]|? ms|
 |61|[Rotate List][Solutions-61]|[WindomZ][Solutions-61-Go]|Medium|[34.0 ns/op/2 test cases][Solutions-61-Test]|? ms|
 |60|[Permutation Sequence][Solutions-60]|[WindomZ][Solutions-60-Go]|Medium|[73.9 ns/op/6 test cases][Solutions-60-Test]|? ms|
@@ -116,6 +117,9 @@ Welcome to report bugs, suggest ideas and discuss on [issues page](https://githu
 ### Support
 If you like it then you can put a :star:Star on it.
 
+[Solutions-63-Test]:solutions/unique_paths_ii/uniquepathsii_test.go#L22
+[Solutions-63-Go]:solutions/unique_paths_ii/uniquepathsii.go
+[Solutions-63]:https://leetcode.com/unique-paths-ii/
 [Solutions-62-Test]:solutions/unique_paths/uniquepaths_test.go#L22
 [Solutions-62-Go]:solutions/unique_paths/uniquepaths.go
 [Solutions-62]:https://leetcode.com/unique-paths/

solutions/unique_paths_ii/README.md

@@ -0,0 +1,29 @@
+# 63. Unique Paths II
+
+[Description](https://leetcode.com/problems/unique-paths-ii/description/) | 
+[Discuss](https://leetcode.com/problems/unique-paths-ii/discuss/) | 
+[Solution](https://leetcode.com/problems/unique-paths-ii/solution/)
+
+## Description
+
+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.

solutions/unique_paths_ii/uniquepathsii.go

@@ -0,0 +1,20 @@
+package uniquepathsii
+
+func uniquePathsWithObstacles(obstacleGrid [][]int) int {
+	if len(obstacleGrid) == 0 {
+		return 0
+	}
+	width := len(obstacleGrid[0])
+	dp := make([]int, width)
+	dp[0] = 1
+	for _, row := range obstacleGrid {
+		for col := 0; col < width; col++ {
+			if row[col] == 1 {
+				dp[col] = 0 // reset current paths to zero if in obstacle space
+			} else if col > 0 {
+				dp[col] += dp[col-1] // add up last paths if in empty space
+			}
+		}
+	}
+	return dp[width-1]
+}

solutions/unique_paths_ii/uniquepathsii_test.go

@@ -0,0 +1,35 @@
+package uniquepathsii
+
+import (
+	"testing"
+
+	"github.com/WindomZ/testify/assert"
+)
+
+func Test_uniquePathsWithObstacles(t *testing.T) {
+	assert.Equal(t, 0,
+		uniquePathsWithObstacles([][]int{}))
+	assert.Equal(t, 2,
+		uniquePathsWithObstacles([][]int{{0, 0}, {0, 0}}))
+	assert.Equal(t, 3,
+		uniquePathsWithObstacles([][]int{{0, 0}, {0, 0}, {0, 0}}))
+	assert.Equal(t, 6,
+		uniquePathsWithObstacles([][]int{{0, 0, 0}, {0, 0, 0}, {0, 0, 0}}))
+	assert.Equal(t, 2,
+		uniquePathsWithObstacles([][]int{{0, 0, 0}, {0, 1, 0}, {0, 0, 0}}))
+}
+
+func Benchmark_uniquePathsWithObstacles(b *testing.B) {
+	b.StopTimer()
+	b.ReportAllocs()
+	b.StartTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			uniquePathsWithObstacles([][]int{})
+			uniquePathsWithObstacles([][]int{{0, 0}, {0, 0}})
+			uniquePathsWithObstacles([][]int{{0, 0}, {0, 0}, {0, 0}})
+			uniquePathsWithObstacles([][]int{{0, 0, 0}, {0, 0, 0}, {0, 0, 0}})
+			uniquePathsWithObstacles([][]int{{0, 0, 0}, {0, 1, 0}, {0, 0, 0}})
+		}
+	})
+}