Added persistent arrays

codes/Data structures/persistent array.cc

@@ -0,0 +1,34 @@
+struct node {
+  node *l, *r;
+  int val;
+
+  node (int x) : l(NULL), r(NULL), val(x) {}
+  node () : l(NULL), r(NULL), val(-1) {}
+};
+
+typedef node* pnode;
+
+pnode update(pnode cur, int l, int r, int at, int what) {
+  pnode ans = new node();
+
+  if (cur != NULL) {
+    *ans = *cur;
+  }
+  if (l == r) {
+    ans-> val = what;
+    return ans;
+  }
+  int m = (l + r) >> 1;
+  if (at <= m) ans-> l = update(ans-> l, l, m, at, what);
+  else ans-> r = update(ans-> r, m + 1, r, at, what);
+  return ans;
+}
+
+int get(pnode cur, int l, int r, int at) {
+  if (cur == NULL) return 0;
+  if (l == r) return cur-> val;
+  int m = (l + r) >> 1;
+  if (at <= m) return get(cur-> l, l, m, at);
+  else         return get(cur-> r, m + 1, r, at);
+}
+

solved/hackerrank/Week of Code 22/Sequential Prefix Function/sol_persistent.cc

@@ -0,0 +1,71 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+#define debug(x) cout << #x " = " << (x) << endl
+
+using namespace std;
+
+const int MLEN = 2 * 100000 + 100;
+const int MN = MLEN * 20; // Mlen * log (Mlen)
+
+struct node {
+  node *l, *r;
+  int val;
+
+  node (int x) : l(NULL), r(NULL), val(x) {}
+  node () : l(NULL), r(NULL), val(-1) {}
+};
+
+typedef node* pnode;
+
+pnode update(pnode cur, int l, int r, int at, int what) {
+  pnode ans = new node();
+
+  if (cur != NULL) {
+    *ans = *cur;
+  }
+  if (l == r) {
+    ans-> val = what;
+    return ans;
+  }
+  int m = (l + r) >> 1;
+  if (at <= m) ans-> l = update(ans-> l, l, m, at, what);
+  else ans-> r = update(ans-> r, m + 1, r, at, what);
+  return ans;
+}
+
+int get(pnode cur, int l, int r, int at) {
+  if (cur == NULL) return 0;
+  if (l == r) return cur-> val;
+  int m = (l + r) >> 1;
+  if (at <= m) return get(cur-> l, l, m, at);
+  else         return get(cur-> r, m + 1, r, at);
+}
+
+pnode version[MLEN];
+int p[MLEN];
+
+int main() {
+  ios_base::sync_with_stdio(false);cin.tie(NULL);
+
+  int n; cin >> n;
+  int len = 0;
+  for (int i = 0; i < n; ++i) {
+    char type; cin >> type;
+    if (type == '-') {
+      len--;
+    } else {
+      int x; cin >> x;
+      if (len == 0) {
+        version[len] = update(NULL, 0, MN, x, 1);
+      } else {
+        int lv = p[len - 1];
+        version[len] = update(version[lv], 0, MN, x, len + 1);
+        p[len] = get(version[lv], 0, MN, x);
+      }
+      len++;
+    }
+    cout << (len > 0 ? p[len - 1] : 0) << endl;
+  }
+
+  return 0;
+}

test/persistent_array.cc

@@ -0,0 +1,34 @@
+struct node {
+  node *l, *r;
+  int val;
+
+  node (int x) : l(NULL), r(NULL), val(x) {}
+  node () : l(NULL), r(NULL), val(-1) {}
+};
+
+typedef node* pnode;
+
+pnode update(pnode cur, int l, int r, int at, int what) {
+  pnode ans = new node();
+
+  if (cur != NULL) {
+    *ans = *cur;
+  }
+  if (l == r) {
+    ans-> val = what;
+    return ans;
+  }
+  int m = (l + r) >> 1;
+  if (at <= m) ans-> l = update(ans-> l, l, m, at, what);
+  else ans-> r = update(ans-> r, m + 1, r, at, what);
+  return ans;
+}
+
+int get(pnode cur, int l, int r, int at) {
+  if (cur == NULL) return 0;
+  if (l == r) return cur-> val;
+  int m = (l + r) >> 1;
+  if (at <= m) return get(cur-> l, l, m, at);
+  else         return get(cur-> r, m + 1, r, at);
+}
+

test/test.sh

@@ -0,0 +1,6 @@
+#! /bin/bash
+
+cp ../codes/Data\ structures/persistent\ array.cc persistent_array.cc
+g++ test_persistent_array.cc -o test_pa
+./test_pa
+rm test_pa

test/test_persistent_array.cc

@@ -0,0 +1,41 @@
+#include <bits/stdc++.h>
+
+#include "persistent_array.cc"
+
+using namespace std;
+
+void free_memory(pnode node) {
+  if (node == NULL) return;
+  free_memory(node->l);
+  free_memory(node->r);
+  delete node;
+}
+
+void random_values() {
+  int max_len = 100;
+  vector<int> data(max_len);
+  pnode root = NULL;
+  for (int i = 0; i < data.size(); ++i) {
+    data[i] = random();
+    root = update(root, 0, max_len, i, data[i]);
+  }
+
+  vector<int> data2 = data;
+  int pos = random() % data.size();
+  data2[pos] = random();
+  pnode ant = root;
+  root = update(root, 0, max_len, pos, data2[pos]);
+  for (int i = 0; i < max_len; ++i) {
+    assert(get(root, 0, max_len, i) == data2[i]);
+    assert(get(ant, 0, max_len, i) == data[i]);
+  }
+}
+
+int main() {
+  int seed = time(NULL);
+  printf("Random seed = %d\n", seed);
+  srand(seed);
+  random_values();
+  printf("Everything OK (random seed = %d).\n", seed);
+  return 0;
+}