Update solution to unique path ii

Author: soapyigu

DP/UniquePathsII.swift

@@ -5,37 +5,29 @@
  */
 
 class UniquePathsII {
-    func uniquePathsWithObstacles(_ obstacleGrid: [[Int]]) -> Int {
-        let m = obstacleGrid.count
-        guard m > 0 else {
-            return 0
-        }
+     func uniquePathsWithObstacles(_ obstacleGrid: [[Int]]) -> Int {
+        let m = obstacleGrid.count, n = obstacleGrid[0].count
 
-        let n = obstacleGrid[0].count
-        guard n > 0 else {
-            return 0
-        }
-    
-        var dp = Array(repeating: Array(repeating: -1, count: n), count: m)
+        var dp = Array(repeating: Array(repeating: 0, count: n), count: m)
 
-        return help(m - 1, n - 1, &dp, obstacleGrid)
-    }
-    
-    fileprivate func help(_ m: Int, _ n: Int, _ dp: inout [[Int]], _ obstacleGrid: [[Int]]) -> Int {
-        if m < 0 || n < 0 {
-            return 0
-        }
-        if obstacleGrid[m][n] == 1 {
-            return 0
-        }
-        if m == 0 && n == 0 {
-            return 1
-        }
-        if dp[m][n] != -1 {
-            return dp[m][n]
+        for i in 0..<m {
+            for j in 0..<n {
+                if obstacleGrid[i][j] == 1 {
+                    dp[i][j] = 0
+                } else {
+                    if i == 0 && j == 0 {
+                        dp[i][j] = 1
+                    } else if i == 0 {
+                        dp[i][j] = dp[i][j - 1]
+                    } else if j == 0 {
+                        dp[i][j] = dp[i - 1][j]
+                    } else {
+                        dp[i][j] = dp[i - 1][j] + dp[i][j - 1]
+                    }
+                }
+            }
         }
 
-        dp[m][n] = help(m - 1, n, &dp, obstacleGrid) + help(m, n - 1, &dp, obstacleGrid)
-        return dp[m][n]
+        return dp[m - 1][n - 1]
     }
 }