Update Swift/62. Unique Paths.swift

Author: liuchuo

Swift/62. Unique Paths.swift

@@ -0,0 +1,20 @@
+// 62. Unique Paths
+// 16 ms, 39.53%
+func uniquePaths(_ m: Int, _ n: Int) -> Int {
+    pathMatrix = Array(repeating: Array(repeating: 0, count: n+1), count: m+1)
+    return pathMatrix(m, n)
+}
+
+private var pathMatrix: [[Int]]!
+private func pathMatrix(_ m: Int, _ n: Int) -> Int {
+    if m <= 0 || n <= 0 { return 0 }
+    if m < 2 || n < 2 { pathMatrix[m][n] = 1; return 1 }
+
+    if pathMatrix[m-1][n] == 0 {
+        pathMatrix[m-1][n] = pathMatrix(m-1, n)
+    }
+    if pathMatrix[m][n-1] == 0 {
+        pathMatrix[m][n-1] = pathMatrix(m, n-1)
+    }
+    return pathMatrix[m-1][n] + pathMatrix[m][n-1]
+}