add trick example of greatest-common-divisor, knuth-morris-pratt, primality-test, quick-pow, split-text

trick/quick-pow.cpp

@@ -0,0 +1,11 @@
+long long quick_pow(int base, int power) {
+    long long ans = 1;
+    while (power > 0) {
+        if (power & 1) {
+            ans *= base;
+        }
+        base *= base;
+        power >>= 1;
+    }
+    return ans;
+}