z algorithm

Author: snuke

z.cpp

@@ -0,0 +1,28 @@
+// Z-algorithm
+// https://snuke.hatenablog.com/entry/2014/12/03/214243
+// https://youtu.be/Uqtxz1KTKOQ?t=9214
+struct Z {
+  int n;
+  string s;
+  vector<int> z;
+  Z() {}
+  Z(const string& s): s(s) { init();}
+  void init() {
+    n = s.size();
+    z = vector<int>(n);
+    z[0] = n;
+    for (int i = 1, j = 0; i < n;) {
+      while (i+j < n && s[i+j] == s[j]) ++j;
+      z[i] = j;
+      if (j) {
+        int k = 1;
+        while (i+k < n && k+z[k] < j) {
+          z[i+k] = z[k];
+          k++;
+        }
+        i += k; j -= k;
+      } else i++;
+    }
+  }
+  int operator[](int i) const { return z[i];}
+};