SPOJ/EPALIN - 4103. Extend to Palindrome/epalin.cpp

   1 // Andrés Mejía
   2 using namespace std;
   3 #include <algorithm>
   4 #include <iostream>
   5 #include <iterator>
   6 #include <numeric>
   7 #include <sstream>
   8 #include <fstream>
   9 #include <cassert>
  10 #include <climits>
  11 #include <cstdlib>
  12 #include <cstring>
  13 #include <string>
  14 #include <cstdio>
  15 #include <vector>
  16 #include <cmath>
  17 #include <queue>
  18 #include <deque>
  19 #include <stack>
  20 #include <list>
  21 #include <map>
  22 #include <set>
  23
  24 #define foreach(x, v) for (typeof (v).begin() x=(v).begin(); x !=(v).end(); ++x)
  25 #define For(i, a, b) for (int i=(a); i<(b); ++i)
  26 #define D(x) cout << #x " is " << x << endl
  27
  28 const double EPS = 1e-9;
  29 int cmp(double x, double y = 0, double tol = EPS) {
  30     return (x <= y + tol) ? (x + tol < y) ? -1 : 0 : 1;
  31 }
  32
  33 const int MAXN = 100005 * 2;
  34
  35 int p[MAXN];
  36
  37 int main(){
  38     string s, t;
  39     s.reserve(MAXN);
  40     t.reserve(MAXN);
  41
  42     while (getline(cin, s)) {
  43         int n = s.size();
  44         t = s + "$" + s;
  45         reverse(t.begin(), t.begin() + n);
  46
  47         p[0] = 0;
  48         for (int i = 1; i < 2 * n + 1; ++i) {
  49             p[i] = p[i - 1];
  50             while (p[i] > 0 and t[i] != t[p[i]]) p[i] = p[p[i] - 1];
  51             if (t[i] == t[p[i]]) p[i]++;
  52         }
  53
  54         // puts("");
  55         // D(t);
  56         // for (int i = 0; i < 2 * n + 1; ++i) {
  57         //     printf("%d ", p[i]);
  58         // }
  59         // puts("");
  60
  61         printf("%s", s.c_str());
  62         for (int i = 0; i <= n; ++i) {
  63             if (2 * i - n >= 0 and p[n + i] >= n - i) {
  64                 //printf("i = %d works on the first case\n", i);
  65                 for (int k = 2 * i - n - 1; k >= 0; --k) {
  66                     putchar(s[k]);
  67                 }
  68                 break;
  69             }
  70
  71             if (i < n and 2 * i - n + 1 >= 0 and p[n + i + 1] >= n - i) {
  72                 for (int k = 2 * i - n; k >= 0; --k) {
  73                     putchar(s[k]);
  74                 }
  75                 break;
  76             }
  77         }
  78         puts("");
  79     }
  80     return 0;
  81 }