add leetcode academicpages#5 and academicpages#6

_posts/2018-07-22-post-1.md

@@ -0,0 +1,46 @@
+---
+title: 'Leetcode#5 Longest Palindromic Substring'
+date: 2018-07-22
+permalink: /posts/leetcode/5
+tags:
+  - Leetcode
+---
+
+## Link: ##
+https://leetcode.com/problems/longest-palindromic-substring/description/#
+
+## Idea: ##
+Dynamic programming:
+DP[i][j] = (s[i] == s[j]) && (j-1 > i ? DP[i+1][j-1] : 1);
+The second case catches len(s[i][j]) == 2 case.
+
+## Solution: ##
+```cpp
+class Solution {
+    public:
+        string longestPalindrome(string s) {
+            if(s.size() <= 1)
+                return s;
+            int max = 1, max_i = 0, max_j = 0, i, j;
+            int n = s.size();
+            bool **DP = (bool**)malloc(n*sizeof(bool*));
+            for(i = 0; i < n; i++)
+                DP[i] = (bool*)malloc(n*sizeof(bool));
+            for(i = 0; i< n; i++)
+                DP[i][i] = true;
+
+            for(i = n - 1; i >= 0; i--) {
+                for(j = i+1; j < n; j++){
+                    DP[i][j] = (s[i] == s[j]) && (j-1 > i ? DP[i+1][j-1] : 1);
+                    if(DP[i][j] && j-i+1 > max) {
+                        max = j-i+1;
+                        max_i = i;
+                        max_j = j;
+                    }
+                }
+            }
+            return s.substr(max_i, max);
+        }
+};
+
+```

_posts/2018-07-22-post-2.md

@@ -0,0 +1,41 @@
+---
+title: 'Leetcode#6 ZigZag Conversion'
+date: 2018-07-22
+permalink: /posts/leetcode/6
+tags:
+  - Leetcode
+---
+
+## Link: ##
+https://leetcode.com/problems/zigzag-conversion/description/
+
+## Idea: ##
+Convert index reversely.
+
+## Solution: ##
+```cpp
+class Solution {
+    public:
+        string convert(string s, int numRows) {
+            if (numRows == 1)
+                return s;
+
+            vector<vector<char>> res(numRows, vector<char>(0, 0));
+
+            int factor = numRows + numRows - 2;
+            for(int i=0; i<s.size(); i++) {
+                int index = i%factor;
+                int row_idx = index < numRows ? index : (factor-index);
+                res[row_idx].push_back(s[i]);
+            }
+
+            string tmp = "";
+            for (int i = 0; i < numRows; i++){
+                for(int j=0; j < res[i].size();j++){
+                    tmp = tmp + res[i][j];
+                }
+            }
+            return tmp;
+        }
+};
+```