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algorithm_interview_course/chapter_two/section_5.cpp

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+/* ************************************************************************
+> File Name:     section_5.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Mon Feb 24 18:44:56 2020
+> Description:   
+ ************************************************************************/
+
+#include <iostream>
+#include <chrono>
+#include <thread>
+using namespace std;
+using namespace chrono;
+
+int fibonacci_1(int n) {
+    if (n <= 0) {
+        return 0;
+    }
+    if (n == 1 || n == 2) {
+        return 1;
+    }
+    int first = 1, second = 1; 
+    int sum = first + second; 
+    for (int i = 2; i < n; i++) {
+        sum = first + second;
+        first = second;
+        second = sum;
+    }
+    return sum;
+}
+
+
+int fibonacci_2(int i) {
+       if(i <= 0) return 0;
+       if(i == 1) return 1;
+       return fibonacci_2(i - 1) + fibonacci_2(i - 2);
+}
+
+int fibonacci_3(int first, int second, int n) {
+    if (n <= 0) {
+        return 0;
+    }
+    if (n < 3) {
+        return 1;
+    }
+    else if (n == 3) {
+        return first + second;
+    }
+    else {
+        return fibonacci_3(second, first + second, n - 1);
+    }
+}
+
+
+void test_fibonacci() {
+    int n;
+    while(cin >> n) {
+        cout << fibonacci_1(n) << endl;
+        cout << fibonacci_2(n) << endl;
+        cout << fibonacci_3(1, 1, n) << endl;
+    } 
+}
+
+int binary_search(int arr[], int l, int r, int n) {
+    if (r >= l) {
+        int mid = l + (r - l) / 2;
+        if (arr[mid] == n)
+            return mid;
+        if (arr[mid] > n)
+            return binary_search(arr, l, mid - 1, n);
+        return binary_search(arr, mid + 1, r, n);
+    }
+    return -1;
+}
+int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
+int binary_search(int l, int r, int n) {
+    if (r >= l) {
+        int mid = l + (r - l) / 2;
+        if (arr[mid] == n)
+            return mid;
+        if (arr[mid] > n)
+            return binary_search(l, mid - 1, n);
+        return binary_search(mid + 1, r, n);
+    }
+    return -1;
+}
+
+void test_binary_search(void) {
+    int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
+    int x = 17;
+    int n = sizeof(arr) / sizeof(arr[0]);
+    // int result = binary_search(arr, 0, n - 1, x);
+    int result = binary_search(0, n - 1, x);
+    (result == -1) ? cout << "Element is not present in array"
+                   : cout << "Element is present at index " << result;
+}
+
+int main()
+{
+    // test_binary_search();
+    // test_fibonacci();
+    return 0;
+}
+