Create decode-the-slanted-ciphertext.cpp

Author: kamyu104

C++/decode-the-slanted-ciphertext.cpp

@@ -0,0 +1,48 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    string decodeCiphertext(string encodedText, int rows) {
+        const int cols = size(encodedText) / rows;
+        int k = size(encodedText);
+        for (int i = cols - 1; i >= 0 && k == size(encodedText); --i) {
+            for (int j = i + ((size(encodedText) - 1) - i) / (cols + 1) * (cols + 1); j >= i; j -= cols + 1) {
+                if (encodedText[j] != ' ') {
+                    k = j;
+                    break;
+                }
+            }
+        }
+        string result;
+        for (int i = 0; i < cols && k != -1; ++i) {
+            for (int j = i; j < size(encodedText); j += cols + 1) {
+                result.push_back(encodedText[j]);
+                if (j == k) {
+                    k = -1;
+                    break;
+                }
+            }
+        }
+        return result;
+    }
+};
+
+// Time:  O(n)
+// Space: O(n)
+class Solution2 {
+public:
+    string decodeCiphertext(string encodedText, int rows) {
+        const int cols = size(encodedText) / rows;
+        string result;
+        for (int i = 0; i < cols; ++i) {
+            for (int j = i; j < size(encodedText); j += cols + 1) {
+                result.push_back(encodedText[j]);
+            }
+        }
+        while (!empty(result) && result.back() == ' ') {
+            result.pop_back();
+        }
+        return result;
+    }
+};