Merge pull request #324 from iamrahul8/patch-1

Added circular palindrome cpp

Author: gantavyamalviya

Dynamic Programming/Circular Palindromes.cpp

@@ -0,0 +1,183 @@
+//Hackerrank Problem - Circular Palindromes
+// Level - Hard
+#include <algorithm>
+#include <iostream>
+#include <cassert>
+#include <cstdlib>
+#include <cstring>
+#include <cstdio>
+#include <cmath>
+#include <queue>
+#include <map>
+#include <set>
+
+using namespace std;
+
+#define type(x) __typeof((x).begin())
+#define foreach(i, x) for(type(x) i = (x).begin(); i != (x).end(); i++)
+#define hash ___hash
+
+typedef long long ll;
+typedef pair < int, int > ii;
+
+const int inf = 1e9 + 333;
+const ll linf = 1e18 + 333;
+
+const int N = 2e6 + 5;
+
+int n;
+char s[N];
+bool h[N];
+int go_odd[N], go_even[N], tmp[N << 1], rad[N << 1], ans[2][N];
+
+void manacher() {
+    memset(tmp, 0, sizeof(tmp));
+    memset(rad, 0, sizeof(rad));
+    int m = n * 2 + 1;
+    for(int i = 0; i < m; i++)
+        tmp[i] = '#';
+    for(int i = 0; i < n; i++)
+        tmp[i * 2 + 1] = s[i + 1];
+    int i = 0, j = 0;
+    while(i < m) {
+        while(i - j >= 0 and i + j < m and tmp[i - j] == tmp[i + j])
+            j++;
+        rad[i] = j;
+        int k = 1;
+        while(rad[i - k] < rad[i] - k) {
+            rad[i + k] = rad[i - k];
+            k++;
+        }
+        i += k;
+        j = max(0, j - k);
+    }
+    for(int i = 1; i <= n; i++)
+        go_odd[i] = rad[(i - 1) * 2 + 1] / 2;//abcba --> go_odd[3] = 3
+    for(int i = 1; i <= n; i++)
+        go_even[i - 1] = rad[(i - 1) * 2] / 2;//abccba --> go_even[3] = 3
+}
+
+void solveOdd(bool w) {
+    int oth = 0;
+    set < ii > go;
+    for(int i = 1; i <= (n + 1) / 2; i++) {
+        go.insert({go_odd[i], i});
+    }
+    for(int i = 1; i <= n; i++) {
+        while(go.size()) {
+            int x = go.rbegin() -> first;
+            int id = go.rbegin() -> second;
+            if(id < i) {
+                go.erase(*go.rbegin());
+                continue;
+            }
+            int mx = (id - i + 1) * 2 - 1;
+            if(x > mx) {
+                oth = max(oth, id);
+                go.erase(*go.rbegin());
+                continue;
+            }
+            break;
+        }
+        if(go.size())
+            ans[w][i] = max(ans[w][i], go.rbegin() -> first);
+        if(oth >= i)
+            ans[w][i] = max(ans[w][i], (oth - i + 1) * 2 - 1);
+        //printf("ans[%d] = %d oth = %d\n", i, ans[w][i]);
+        int add = (n + 1) / 2 + i;
+        go.insert({go_odd[add], add});
+    }
+}
+
+int get(int x, int y) {
+    y -= x - 1;
+    return min(y, n - y) * 2;
+}
+
+void solveEven(bool w) {
+    int oth = 0;
+    set < ii > go;
+    for(int i = 1; i <= (n + 1) / 2; i++) {
+        go.insert({go_even[i], i});
+    }
+    for(int i = 1; i <= n; i++) {
+        while(go.size()) {
+            int x = go.rbegin() -> first;
+            int id = go.rbegin() -> second;
+            if(id < i) {
+                go.erase(*go.rbegin());
+                continue;
+            }
+            int mx = get(i, id);
+            if(x > mx) {
+                oth = max(oth, id);
+                go.erase(*go.rbegin());
+                continue;
+            }
+            break;
+        }
+        if(go.size())
+            ans[w][i] = max(ans[w][i], go.rbegin() -> first);
+        if(oth >= i)
+            ans[w][i] = max(ans[w][i], get(i, oth));
+        //printf("ans[%d] = %d\n", i, ans[w][i]);
+        int add = (n + 1) / 2 + i;
+        go.insert({go_even[add], add});
+    }
+}
+
+
+int main () {
+    
+    scanf("%d %s", &n, s + 1);
+    
+    for(int i = 1; i <= n; i++)
+        s[i + n] = s[i];
+    
+    
+    n *= 2;
+    manacher();
+    n /= 2;
+    
+    for(int i = 1; i <= n + n; i++) {
+        go_odd[i] *= 2;
+        go_odd[i] -= 1;
+        go_even[i] *= 2;
+    }
+    
+    solveOdd(0);
+    solveEven(0);
+    
+  
+    
+    reverse(s + 1, s + n * 2 + 1);
+    
+    n *= 2;
+    manacher();
+    n /= 2;
+    
+    for(int i = 1; i <= n + n; i++) {
+        go_odd[i] *= 2;
+        go_odd[i] -= 1;
+        go_even[i] *= 2;
+    }
+    
+    solveOdd(1);
+    solveEven(1);
+   
+    printf("%d\n", max(ans[0][1], ans[1][1]));
+    
+    for(int i = 2; i <= n; i++) {
+        printf("%d\n", max(ans[0][i], ans[1][n + 2 - i]));
+    }
+    
+    return 0;
+    
+}
+
+
+
+
+
+
+