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algorithm_interview_course/chapter_two/section_3.cpp

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+/* ************************************************************************
+> File Name:     section_3.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Sat Feb  8 22:00:32 2020
+> Description:   
+ ************************************************************************/
+
+#include<iostream>
+using namespace std;
+
+int function1(int x, int n) {
+    int result = 1;  // 注意 任何数的0次方等于1 
+    for (int i = 0; i < n; i++) {
+        result = result * x;
+    }
+    return result;
+}
+
+int function2(int x, int n) {
+    if (n == 0) {
+        return 1; // return 1 同样是因为0次方是等于1的
+    }
+    return function2(x, n - 1) * x;
+}
+
+int function3(int x, int n) {
+    if (n == 0) {
+        return 1;
+    }
+    // if (n == 1) { // 这里如果不作处理就会陷入死循环
+    //     return x;
+    // }
+    if (n % 2 == 1) {
+        return function3(x, n/2) * function3(x, n/2) * x;
+    } 
+    return function3(x, n/2) * function3(x, n/2);
+}
+
+int function4(int x, int n) {
+    if (n == 0) {
+        return 1;
+    }
+    int t = function4(x, n/2);
+    if (n % 2 == 1) {
+        return t*t*x;
+    } 
+    return t*t;
+}
+int main() {
+    int x, n;
+    while (cin >> x >> n) {
+        cout << function3(x, n) << endl;
+    }
+}