Create heozeop.cpp

Author: heozeop

decode-ways/heozeop.cpp

@@ -0,0 +1,31 @@
+// Time Complexity: O(n)
+// Spatial Complexity: O(n)
+
+class Solution {
+public:
+  int numDecodings(string s) {
+    if(s.length() < 1 || s[0] == '0') {
+      return 0;
+    }
+
+    vector<int> dp(s.length() + 1, 0);
+    dp[0] = dp[1] = 1;
+    if(s[1] == '0') {
+      dp[1] = 0;
+    }
+
+    int prev,pprev;
+    for(int i = 2; i <= s.length(); ++i) {
+      prev = s[i - 1] - '0';
+      if (prev <= 9 && prev > 0) {
+        dp[i] += dp[i-1];
+      }
+      pprev = (s[i - 2] - '0') * 10 + prev;
+      if(pprev <= 26 && pprev > 9) {
+        dp[i] += dp[i-2];
+      }
+    }
+
+    return dp[s.length()];
+  }
+};