새싹교실/2020/이찌반/전성수

약수의 합

#include <stdbool.h>
#include <stdlib.h>

int solution(int n) {
    int answer = 0;
    for (int i = n; i > 0; i--) {
        if (n % i == 0) {
            answer += i;
        }
        else continue;
    }
    return answer;
}

하샤드수

#include <stdbool.h>
#include <stdlib.h>

bool solution(int x) {
    bool answer = true;
    int sum = 0;
    while (1) {
        sum += x % 10;
        if (x / 10 < 10) {
            sum += x / 10;
            break;
        }
        else {
            x /= 10;
        }
    }
    if (x % sum == 0) answer = true;
    else  answer = false;

    return answer;
}

수박수박수

#include <stdbool.h>
#include <stdlib.h>

bool solution(int x) {
    bool answer = true;
    int sum = 0;
    while (1) {
        sum += x % 10;
        if (x / 10 < 10) {
            sum += x / 10;
            break;
        }
        else {
            x /= 10;
        }
    }
    if (x % sum == 0) answer = true;
    else  answer = false;

    return answer;
}

두개 뽑아서 더하기

#include <stdbool.h>
#include <stdlib.h>
#define SWAP(a, b) {int t = a; a = b; b = t;}

int* solution(int numbers[], size_t numbers_len) {
    int length = 0;
    int* answer = (int*)malloc(sizeof(int) * 100);
    for (int i = 0; i < numbers_len - 1; i++) {
        for (int j = i + 1; j < numbers_len; j++) {
            int add = numbers[i] + numbers[j];
            int check = 1;
            for (int k = 0; k < length; k++) {
                if (answer[k] == add) check = 0;
            }
            if (check == 1) {
                answer[length] = add;
                length++;
            }
        }
    }
    for (int i = 0; i < length; i++) {
        for (int j = 0; j < length - 1; j++) {
            if (answer[j] > answer[j + 1]) SWAP(answer[j], answer[j + 1]);
        }
    }
    return answer;
}

- 별찍기

int main(void) {
    int a;
    int b;
    scanf_s("%d %d", &a, &b);
    printf("%d\n", a + b);
    for (int i = 0; i < b; i++) {

        for (int j = 0; j < a; j++) {
            printf("*");
        }

        printf("\n");
    }
    return 0;
}

문자열 정렬

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#define SWAP(a,b) {int t = a;a = b;b = t;}
char* solution(const char* s) {
    int cnt = strlen(s);
    char* answer = (char*)malloc(sizeof(char) * cnt);
    for (int i = 0; i <= cnt; i++) {
        answer[i] = s[i];
    }
    for (int i = 0; i < cnt; i++) {
        for (int j = 0; j < cnt - 1; j++) {
            if (answer[j] <= answer[j + 1]) {
                SWAP(answer[j], answer[j + 1]);
            }
        }
    }
    return answer;
}

문자열을 정수로 바꾸기

#include <stdbool.h>
#include <stdlib.h>

int solution(const char* s) {
    int answer = 0;
    answer = atoi(s);
    return answer;
}

문자열 다루기

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

bool solution(const char* s) {
    bool answer = true;
    int count = strlen(s);

    for (int i = 0; i < count; i++) {
        if (isalpha(s[i])) {
            answer = false;
        }
    }
    if ((count == 4 || count == 6) != 1) {
        answer = false;
    }

    return answer;
}

두 정수 사이의 합

#include <stdbool.h>
#include <stdlib.h>

long long solution(int a, int b) {
    long long answer = 0;
    long long sum = 0;
    if (a > b) {
        for (int i = b; i <= a; i++) {
            sum += i;
        }
        answer = sum;
    }
    else if (a < b) {
        for (int i = a; i <= b; i++) {
            sum += i;
        }
        answer = sum;
    }
    else {
        answer = a;
    }
    return answer;
}

가운데 글자 가져오기

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

char* solution(const char* s) {
    char* answer;
    int cnt = strlen(s);
    if (cnt % 2) {
        answer = (char*)malloc(sizeof(char));
        answer[0] = s[cnt / 2];
        answer[1] = '\0';
    }
    else {
        answer = (char*)malloc(sizeof(char) * 2);
        answer[0] = s[(cnt / 2) - 1];
        answer[1] = s[cnt / 2];
        answer[2] = '\0';
    }
    return answer;
}

2016년

#include <stdbool.h>
#include <stdlib.h>
char* solution(int a, int b) {
    char* answer = (char*)malloc(sizeof(char) * 10);
    int day = b;
    int month[] = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    for (int i = 0; i < a; i++) {
        day += month[i - 1];
    }
    switch (day % 7) {
    case 0: answer = "THU"; break;
    case 1: answer = "FRI"; break;
    case 2: answer = "SAT"; break;
    case 3: answer = "SUN"; break;
    case 4: answer = "MON"; break;
    case 5: answer = "TUE"; break;
    case 6: answer = "WED"; break;
    }
    return answer;
}

자릿수 더하기

#include <stdbool.h>
#include <stdlib.h>

int solution(int n) {
    int answer = 0;
    while (1) {
        answer += n % 10;
        n /= 10;
        if (n / 10 == 0) {
            answer += n;
            break;
        }

    }
    return answer;
}

자연수를 뒤집어 배열로 만들기

#include <stdbool.h>
#include <stdlib.h>

int* solution(long long n) {
    int i = 0;
    int* answer = (int*)malloc(sizeof(int) * 11);
    do {
        answer[i++] = n % 10;
        n /= 10;
    } while (n > 0);

    return answer;
}