#21 complete!

Co-authored-by: sigonasr2 <sigonasr2@gmail.com>

archives/21/src/main.c

@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include "utils.h"
+
+/*
+    Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
+    If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.
+
+    For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
+
+    Evaluate the sum of all the amicable numbers under 10000.
+
+    https://projecteuler.net/problem=21
+*/
+
+int main(int argc,char**argv) {
+    int counter=1;
+    long totalSum=0;
+    while (counter<10000) {
+        //printf("Factor sum of %d: 1,",counter);
+        int factorSum=1;
+        int max=counter/2;
+        for (int i=2;i<max;i++) {
+            if (counter%i==0) {
+                factorSum+=i;
+                if (i!=(counter/i)) {
+                    factorSum+=counter/i;
+                }
+                max=counter/i;
+                //printf("%d,%d,",i,counter/i);
+            }
+        }
+        //printf("\n");
+        int factorSum2=1;
+        max=factorSum/2;
+        for (int i=2;i<max;i++) {
+            if (factorSum%i==0) {
+                factorSum2+=i;
+                factorSum2+=factorSum/i;
+                max=factorSum/i;
+            }
+        }
+        if (factorSum!=factorSum2&&counter==factorSum2) {
+            printf("%d\n",counter);
+            totalSum+=counter;
+        }
+        counter++;
+    }
+    printf("\n\nAmicable Number sum: %ld",totalSum);
+    return 0;
+}

archives/21/src/utils.c

@@ -0,0 +1,72 @@
+#include "utils.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+struct String add(struct String numb1, struct String numb2){
+    byte carryover=0;
+    int digitCount=0;
+    char*str = malloc(0);
+    if (numb1.length>=numb2.length) {
+        for (int offset=0;offset<numb1.length;offset++) {
+            str = realloc(str,++digitCount);
+            //printf("Digit count is now %d\n",digitCount);
+            if (numb2.length>offset) {
+                //printf("%c %c\n",numb1.str[numb1.length-offset-1],numb2.str[numb2.length-offset-1]);
+                int sum=((numb1.str[numb1.length-offset-1]-'0')+(numb2.str[numb2.length-offset-1]-'0'))+((carryover>0)?carryover--:0);
+                if (sum>=10) {
+                    carryover=1;
+                    sum-=10;
+                }
+                str[offset]=sum+'0';
+            } else {
+                str[offset]=numb1.str[numb1.length-offset-1];
+            }
+        }
+    } else {
+        for (int offset=0;offset<numb2.length;offset++) {
+            str = realloc(str,++digitCount);
+            //printf("Digit count is now %d\n",digitCount);
+            if (numb1.length>offset) {
+                //printf("%c %c\n",numb1.str[numb1.length-offset-1],numb2.str[numb2.length-offset-1]);
+                int sum=((numb1.str[numb1.length-offset-1]-'0')+(numb2.str[numb2.length-offset-1]-'0'))+((carryover>0)?carryover--:0);
+                if (sum>=10) {
+                    carryover=1;
+                    sum-=10;
+                }
+                str[offset]=sum+'0';
+            } else {
+                str[offset]=numb2.str[numb2.length-offset-1];
+            }
+        }
+    }
+    if (carryover>0) {
+        str = realloc(str,++digitCount);
+        str[digitCount-1]='1';
+    }
+    for (int i=0;i<digitCount/2;i++) {
+        char c = str[i];
+        char c2 = str[digitCount-i-1];
+        str[digitCount-i-1]=c;
+        str[i]=c2;
+    }
+    struct String newStr = {digitCount,str};
+    return newStr;
+}
+
+void printLongDoubleArr(int a,int b,long doubleArr[a][b]) {
+    for (int i=0;i<a;i++) {
+        for (int j=0;j<b;j++) {
+            printf("%ld\t",doubleArr[i][j]);
+        }
+        printf("\n");
+    }
+}
+
+void printIntDoubleArr(int a,int b,int doubleArr[a][b]) {
+    for (int i=0;i<a;i++) {
+        for (int j=0;j<b;j++) {
+            printf("%d\t",doubleArr[i][j]);
+        }
+        printf("\n");
+    }
+}

archives/21/src/utils.h

@@ -0,0 +1,11 @@
+#define true 1
+#define false 0
+#define boolean char
+#define byte char
+struct String{
+    int length;
+    char*str;
+};
+struct String add(struct String numb1, struct String numb2);
+void printLongDoubleArr(int a,int b,long doubleArr[a][b]);
+void printIntDoubleArr(int a,int b,int doubleArr[a][b]);

src/main.c

@@ -2,88 +2,49 @@
 #include "utils.h"
 
 /*
-    You are given the following information, but you may prefer to do some research for yourself.
+    Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
+    If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.
 
-    1 Jan 1900 was a Monday.
-    Thirty days has September,
-    April, June and November.
-    All the rest have thirty-one,
-    Saving February alone,
-    Which has twenty-eight, rain or shine.
-    And on leap years, twenty-nine.
-    A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
-    How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
+    For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
 
-    https://projecteuler.net/problem=19
-*/
-
-enum Month {JANUARY=1,FEBRUARY,MARCH,APRIL,MAY,JUNE,JULY,AUGUST,SEPTEMBER,OCTOBER,NOVEMBER,DECEMBER};
+    Evaluate the sum of all the amicable numbers under 10000.
 
-int DaysInMonth(enum Month month,int year) {
-    switch (month) {
-        case JANUARY:
-        case MARCH:
-        case MAY:
-        case JULY:
-        case AUGUST:
-        case OCTOBER:
-        case DECEMBER:{
-            return 31;
-        }break;
-        case APRIL:
-        case JUNE:
-        case SEPTEMBER:
-        case NOVEMBER:{
-            return 30;
-        }break;
-        case FEBRUARY:{
-            return ((year%100==0)&&(year%400!=0))?28:(year%4==0)?29:28;
-        }break;
-    }
-}
+    https://projecteuler.net/problem=21
+*/
 
 int main(int argc,char**argv) {
-    int day=1;
-    enum Month month=1;
-    int year=1900;
-    enum Weekday{
-        SUNDAY,
-        MONDAY,
-        TUESDAY,
-        WEDNESDAY,
-        THURSDAY,
-        FRIDAY,
-        SATURDAY,
-    } weekday=MONDAY;
-
-    int sundayCount=0;
-
-    while((day!=31)||(month!=12)||(year!=2000)) {
-        printf("Date: %d/%d/%d\n",month,day,year);
-        if (year>=1901) {
-            //Start counting Sundays.
-            if (weekday==SUNDAY&&day==1) {
-                sundayCount++;
+    int counter=1;
+    long totalSum=0;
+    while (counter<10000) {
+        //printf("Factor sum of %d: 1,",counter);
+        int factorSum=1;
+        int max=counter/2;
+        for (int i=2;i<max;i++) {
+            if (counter%i==0) {
+                factorSum+=i;
+                if (i!=(counter/i)) {
+                    factorSum+=counter/i;
+                }
+                max=counter/i;
+                //printf("%d,%d,",i,counter/i);
+            }
+        }
+        //printf("\n");
+        int factorSum2=1;
+        max=factorSum/2;
+        for (int i=2;i<max;i++) {
+            if (factorSum%i==0) {
+                factorSum2+=i;
+                factorSum2+=factorSum/i;
+                max=factorSum/i;
             }
         }
-        //Increment the day.
-        if (day+1<=DaysInMonth(month,year)) {
-            day++;
-        } else 
-        if (month+1<=12){
-            //It's a new month.
-            month++;
-            day=1;
-        } else {
-            //It's a new year!
-            year++;
-            day=1;
-            month=1;
-            //printf("The year is now %d...\n",year);
+        if (factorSum!=factorSum2&&counter==factorSum2) {
+            printf("%d\n",counter);
+            totalSum+=counter;
         }
-        weekday=((weekday+1)<=SATURDAY)?weekday+1:SUNDAY;
+        counter++;
     }
-
-    printf("\n\n%d Sundays were on the 1st of the month.",sundayCount);
+    printf("\n\nAmicable Number sum: %ld",totalSum);
     return 0;
 }