Leetcode day 2 and 3

leetcode/lc6/notes.md

@@ -0,0 +1,5 @@
+We can use 2D array instead of vector of vectors but prefer vector<vector<char>> when 
+It has to grow dynamically
+Different rows have different lengths
+To save memory
+

leetcode/lc6/zigzag.cpp

@@ -0,0 +1,24 @@
+class Solution{
+    public:
+        string convert(string s,int numrows){
+            if(numrows == 0|| numsrows>=s.length())
+                return s;
+            vector<vector<char>> rows(numrows);
+            int index = 0, direc = 1;
+
+            for(char c: s){
+                rows[index].push_back(c);
+                if(index == 0)
+                    direc =1;
+                else if(index == numrows -1)
+                    direc = -1;
+                index+=direc;
+            }
+            string res;
+            for(const auto &row : rows)
+                for(char c : row)
+                    res+=c;
+
+            return res;
+        }
+};