Lesson 8.

08/Exercise01.c

@@ -63,6 +63,7 @@ int main() {
     for (i = 0; i < 40; i++) {
         people[i] = ALIVE;
     }
+
     startTime = clock();
     printf("Stand at %d\n",recursion(0,0)+1);
     finishTime = clock();

08/Exercise02.c

@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <time.h>
+
+int goDown(int n) {
+    if (n == 1) {
+        return 1;
+    }
+    else if (n == 2) {
+        return 2;
+    }
+    else if (n == 3) {
+        return 4;
+    }
+    else {
+        return goDown(n-1) + goDown(n-2) + goDown(n-3);
+    }
+}
+
+int main() {
+    int n = 0;
+    int i = 0, j = 0;
+    int startTime, finishTime;
+    double time;
+    double timeSum;
+    int ans;
+    for (i = 5; i < 21; i++) {
+        printf("%d: %d\n", i, goDown(i));
+    }
+    for (j = 15; j <=35; j+=10) {
+        printf("n = %d\n", j);
+        for (i = 0; i < 3; i++) {
+            startTime = clock();
+            ans = goDown(j);
+            finishTime = clock();
+            time = ((double)finishTime - startTime) / CLOCKS_PER_SEC;
+            timeSum += time;
+            printf("%.16lf\n", time);
+        }
+        printf("Avg: %lf\n", timeSum/3);
+        timeSum = 0;
+    }
+    return 0;
+}

08/Optional01.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+
+
+bool checkDigits(int chicken, int rabbit) {
+    bool digits[6] = {0};
+    int num = chicken*1000 + rabbit;
+    while (num > 0) {
+        if (num % 10 > 6 || digits[num % 10]) {
+            return false;
+        }
+        else {
+            digits[num % 10] = true;
+            num /= 10;
+        }
+    }
+    return true;
+}
+
+int main() {
+    int count = 50;
+    for (count = 50; count < 250; count++) {
+        if (checkDigits(count * 2, count * 4)) {
+            printf("There are %d chickens and rabbits. %d chicken legs, %d rabbit legs.", count, count*2, count*4);
+        }
+    }
+    return 0;
+}

08/Optional02.c

@@ -0,0 +1,36 @@
+#include <stdio.h>
+
+int sumSquares(int num) {
+    if (num == 1) {
+        return 1;
+    }
+    else {
+        return num*num + sumSquares(num - 1);
+    }
+}
+
+int sumSum(int k) {
+    if (k == 1) {
+        return 1;
+    }
+    else {
+        return k*sumSquares(k) + sumSum(k - 1);
+    }
+}
+
+int main() {
+    int S, NS;
+    int n = 50;
+    S = sumSum(n);
+    NS = n*(n+1)/2*(n+2)/3*(8*n*n+11*n + 1)/20;
+    if (S > NS) {
+        printf("1");
+    }
+    else if (S == NS) {
+        printf("0");
+    }
+    else {
+        printf("-1");
+    }
+    return 0;
+}

08/test.cpp

@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+#ifndef __x86_64__
+#define __x86_64__ 0
+#endif
+
+
+int main() {
+    printf("x86_64: %d\n", __x86_64__);
+    printf("arm64: %d\n", __arm64__);
+    printf("macOS: %d\n", __MAC_13_0);
+    int a=0;
+    printf("%d", 5/a);
+    return 0;
+}