Add longest palindrom substring test case

Author: xiangzhai

palindrome/SConstruct

@@ -0,0 +1,3 @@
+env = Environment(CCFLAGS='-g')
+
+env.Program('palin_str.cpp')

palindrome/gettysburg.txt

@@ -0,0 +1 @@
+FourscoreandsevenyearsagoourfaathersbroughtforthonthiscontainentanewnationconceivedinzLibertyanddedicatedtothepropositionthatallmenarecreatedequalNowweareengagedinagreahtcivilwartestingwhetherthatnaptionoranynartionsoconceivedandsodedicatedcanlongendureWeareqmetonagreatbattlefiemldoftzhatwarWehavecometodedicpateaportionofthatfieldasafinalrestingplaceforthosewhoheregavetheirlivesthatthatnationmightliveItisaltogetherfangandproperthatweshoulddothisButinalargersensewecannotdedicatewecannotconsecratewecannothallowthisgroundThebravelmenlivinganddeadwhostruggledherehaveconsecrateditfaraboveourpoorponwertoaddordetractTgheworldadswfilllittlenotlenorlongrememberwhatwesayherebutitcanneverforgetwhattheydidhereItisforusthelivingrathertobededicatedheretotheulnfinishedworkwhichtheywhofoughtherehavethusfarsonoblyadvancedItisratherforustobeherededicatedtothegreattdafskremainingbeforeusthatfromthesehonoreddeadwetakeincreaseddevotiontothatcauseforwhichtheygavethelastpfullmeasureofdevotionthatweherehighlyresolvethatthesedeadshallnothavediedinvainthatthisnationunsderGodshallhaveanewbirthoffreedomandthatgovernmentofthepeoplebythepeopleforthepeopleshallnotperishfromtheearth

palindrome/palin_str.cpp

@@ -0,0 +1,77 @@
+#include <iostream>
+#include <fstream>
+#include <algorithm>
+
+std::string m_preProcess(std::string s) 
+{
+    int n = s.length();
+    if (n == 0) return "^$";
+    std::string ret = "^";
+    for (int i = 0; i < n; i++)
+        ret += "#" + s.substr(i, 1);
+ 
+    ret += "#$";
+    return ret;
+}
+ 
+std::string longestPalindrome(std::string s) 
+{
+    std::string T = m_preProcess(s);
+    int n = T.length();
+    int *P = new int[n];
+    int C = 0, R = 0;
+    for (int i = 1; i < n - 1; i++) 
+    {
+        int i_mirror = 2 * C - i; // equals to i' = C - (i-C)
+    
+        P[i] = (R > i) ? std::min(R-i, P[i_mirror]) : 0;
+    
+        // Attempt to expand palindrome centered at i
+        while (T[i + 1 + P[i]] == T[i - 1 - P[i]])
+            P[i]++;
+ 
+        // If palindrome centered at i expand past R,
+        // adjust center based on expanded palindrome.
+        if (i + P[i] > R) 
+        {
+            C = i;
+            R = i + P[i];
+        }
+    }
+ 
+    // Find the maximum element in P.
+    int maxLen = 0;
+    int centerIndex = 0;
+    for (int i = 1; i < n - 1; i++) 
+    {
+        if (P[i] > maxLen) 
+        {
+            maxLen = P[i];
+            centerIndex = i;
+        }
+    }
+    delete[] P;
+  
+    return s.substr((centerIndex - 1 - maxLen) / 2, maxLen);
+}
+
+int main(int argc, char* argv[]) 
+{
+    std::ifstream file("gettysburg.txt");
+    std::string ori_str;
+    std::string longest_parlin_str;
+    std::string color_str;
+    int find_pos = 0;
+
+    file >> ori_str;
+    longest_parlin_str = longestPalindrome(ori_str);
+    find_pos = ori_str.find(longest_parlin_str);
+
+    color_str = ori_str.substr(0, find_pos) + "\033[33m" + longest_parlin_str 
+        + "\033[0m" + ori_str.substr(find_pos + longest_parlin_str.size(), 
+                ori_str.size() - find_pos - longest_parlin_str.size());
+
+    std::cout << color_str << std::endl;
+
+    return 0;
+}