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

trick/greatest-common-divisor.cpp

@@ -0,0 +1,8 @@
+int greatest_common_divisor(int num1, int num2) {
+	while (num2 != 0) {
+		int temp = num2;
+		num2 = num1 % num2;
+		num1 = temp;
+	}
+	return num1;
+}

trick/knuth-morris-pratt.cpp

@@ -0,0 +1,29 @@
+#include <vector>
+#include <string>
+
+int knuth_morris_pratt(const std::string text, const std::string pattern) {
+	int n = text.length(), m = pattern.length();
+	std::vector<int> next(m, 0);
+	for (int i = 1, j = 0; i < m; i++) {
+		while (j > 0 && pattern[i] != pattern[j]) {
+			j = next[j - 1];
+		}
+		if (pattern[i] == pattern[j]) {
+			j++;
+		}
+		next[i] = j;
+	}
+
+	for (int i = 0, j = 0; i < n; i++) {
+		while (j > 0 && text[i] != pattern[j]) {
+			j = next[j - 1];
+		}
+		if (text[i] == pattern[j]) {
+			j++;
+		}
+		if (j == m) {
+			return i - m + 1;
+		}
+	}
+	return -1;
+}

trick/primality-test.cpp

@@ -0,0 +1,17 @@
+#include <vector>
+
+bool primality_check(int n) {
+	std::vector<bool> is_prime(n + 1, true);
+	if (n <= 2) {
+		return false;
+	}
+	is_prime[0] = is_prime[1] = false;
+	for (int i = 2; i * i <= n; i++) {
+		if (is_prime[i]) {
+			for (int j = i * i; j <= n; j += i) {
+				is_prime[j] = false;
+			}
+		}
+	}
+	return is_prime[n];
+}

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;
+}

trick/split-text.cpp

@@ -0,0 +1,13 @@
+#include <vector>
+#include <string>
+
+std::vector<std::string> split(std::string target, std::string pattern) {
+    std::vector<std::string> res;
+    size_t start = 0, next = 0;
+    while ((next = target.find(pattern, start)) != std::string::npos) {
+        res.push_back(target.substr(start, next - start));
+        start = next + pattern.length();
+    }
+    res.push_back(target.substr(start));
+    return res;
+}