decode ways solution

Author: yhkee0404

decode-ways/yhkee0404.go

@@ -0,0 +1,20 @@
+func numDecodings(s string) int {
+    dp := make([]int, len(s) + 1)
+    dp[0] = 1
+    const cnt = rune('Z') - rune('A') + 1
+    for i, c := range s {
+        a := 0
+        if i != 0 {
+            b := (rune(s[i - 1]) - rune('0')) * 10 + rune(c) - rune('0')
+            if b > 9 && b <= cnt {
+                a += dp[i - 1]
+            }
+        }
+        b := rune(c) - rune('0')
+        if b != 0 && b < cnt {
+            a += dp[i]
+        }
+        dp[i + 1] = a
+    }
+    return dp[len(s)]
+}