From a563e94d33c76f39626f60ae387a4c0953d9a0fc Mon Sep 17 00:00:00 2001
From: prasanna <mondiprasanna8@gmail.com>
Date: Wed, 26 Nov 2025 14:47:35 +0530
Subject: [PATCH] Implement numDecodings function for decoding ways

---
 decode.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 decode.c

diff --git a/decode.c b/decode.c
new file mode 100644
index 0000000..c63ee84
--- /dev/null
+++ b/decode.c
@@ -0,0 +1,32 @@
+int numDecodings(char *s) {
+    int n = strlen(s);
+    if (n == 0 || s[0] == '0')
+        return 0;
+
+    int dp_prev2 = 1;  // dp[i-2]
+    int dp_prev1 = 1;  // dp[i-1]
+
+    for (int i = 1; i < n; i++) {
+        int dp_current = 0;
+
+        // Case 1: Single digit decode (must not be '0')
+        if (s[i] != '0') {
+            dp_current += dp_prev1;
+        }
+
+        // Case 2: Two-digit decode (10 to 26)
+        int twoDigit = (s[i - 1] - '0') * 10 + (s[i] - '0');
+        if (twoDigit >= 10 && twoDigit <= 26) {
+            dp_current += dp_prev2;
+        }
+
+        // If no valid decoding
+        if (dp_current == 0)
+            return 0;
+
+        dp_prev2 = dp_prev1;
+        dp_prev1 = dp_current;
+    }
+
+    return dp_prev1;
+}