decode-ways solution

Author: ohgyulim

decode-ways/ohgyulim.java

@@ -0,0 +1,26 @@
+class Solution {
+    /* 시간 복잡도: O(N)
+    * - for 루프: O(N)
+    * 공간 복잡도: O(N), dp배열
+    */ 
+    public int numDecodings(String s) {
+        if (s.charAt(0) == '0') return 0;
+        int[] dp = new int[s.length() + 1];
+        dp[0] = 1;
+        dp[1] = 1;
+
+        for (int i = 2; i <= s.length(); i++) {
+            int one = Integer.parseInt(s.substring(i - 1, i));
+            int two = Integer.parseInt(s.substring(i - 2, i));
+
+            if (one > 0) {
+                dp[i] += dp[i - 1];
+            }
+            if (two >= 10 && two <= 26) {
+                dp[i] += dp[i - 2];
+            }
+        }
+        return dp[s.length()];
+    }
+}
+