Add problem PRIME1 from codechef

Author: jhonber

codechef/PRIME1.cpp

@@ -0,0 +1,57 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+const int mx = 1e9 + 10;
+vector<int> primes;
+
+void gen() {
+  primes.push_back(2);
+  for (int p = 3; p * p <= mx; p += 2) {
+    int i = 2;
+    int f = true;
+    while (i * i <= p) {
+      if (p % i == 0) {
+        f = false;
+        break;
+      }
+      i ++;
+    }
+
+    if (f) primes.push_back(p);
+  }
+}
+
+bool isPrime(int x) {
+  if (x == 2) return true;
+
+  int i = 0;
+  while (i < primes.size() && primes[i] * primes[i] <= x) {
+    if (x % primes[i] == 0) return false;
+    i ++;
+  }
+  return true;
+}
+
+int main() {
+  gen();
+  int t;
+  scanf("%d", &t);
+
+  int n, m;
+  while (t --> 0) {
+    scanf("%d %d", &n, &m);
+
+    if (n <= 2) {
+      printf("2\n");
+      n = 3;
+    }
+
+    if (n % 2 == 0) n ++;
+    for (int i = n; i <= m; i += 2) {
+      if (isPrime(i)) printf("%d\n", i);
+    }
+    printf("\n");
+  }
+
+  return 0;
+}