题解 | #24点运算#

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

char sign[3];
int num[4];
int sum = 0;
int left = 4;

// 判断是否可以通过某种运算组合得到 24
bool calculate(int card[]) {
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4; j++) {
            if (j == i) continue;
            for (int k = 0; k < 4; k++) {
                if (k == i || k == j) continue;
                for (int l = 0; l < 4; l++) {
                    if (l == i || l == j || l == k) continue;
                    int tempCard[4] = {card[i], card[j], card[k], card[l]};
                    for (int op1 = 0; op1 < 4; op1++) {
                        for (int op2 = 0; op2 < 4; op2++) {
                            for (int op3 = 0; op3 < 4; op3++) {
                                int tempSum = tempCard[0];
                                switch (op1) {
                                    case 0:
                                        tempSum += tempCard[1];
                                        break;
                                    case 1:
                                        tempSum -= tempCard[1];
                                        break;
                                    case 2:
                                        tempSum *= tempCard[1];
                                        break;
                                    case 3:
                                        tempSum /= tempCard[1];
                                        break;
                                }
                                switch (op2) {
                                    case 0:
                                        tempSum += tempCard[2];
                                        break;
                                    case 1:
                                        tempSum -= tempCard[2];
                                        break;
                                    case 2:
                                        tempSum *= tempCard[2];
                                        break;
                                    case 3:
                                        tempSum /= tempCard[2];
                                        break;
                                }
                                switch (op3) {
                                    case 0:
                                        tempSum += tempCard[3];
                                        break;
                                    case 1:
                                        tempSum -= tempCard[3];
                                        break;
                                    case 2:
                                        tempSum *= tempCard[3];
                                        break;
                                    case 3:
                                        tempSum /= tempCard[3];
                                        break;
                                }
                                if (tempSum == 24) {
                                    num[0] = tempCard[0];
                                    num[1] = tempCard[1];
                                    num[2] = tempCard[2];
                                    num[3] = tempCard[3];
                                    switch (op1) {
                                        case 0:
                                            sign[0] = '+';
                                            break;
                                        case 1:
                                            sign[0] = '-';
                                            break;
                                        case 2:
                                            sign[0] = '*';
                                            break;
                                        case 3:
                                            sign[0] = '/';
                                            break;
                                    }
                                    switch (op2) {
                                        case 0:
                                            sign[1] = '+';
                                            break;
                                        case 1:
                                            sign[1] = '-';
                                            break;
                                        case 2:
                                            sign[1] = '*';
                                            break;
                                        case 3:
                                            sign[1] = '/';
                                            break;
                                    }
                                    switch (op3) {
                                        case 0:
                                            sign[2] = '+';
                                            break;
                                        case 1:
                                            sign[2] = '-';
                                            break;
                                        case 2:
                                            sign[2] = '*';
                                            break;
                                        case 3:
                                            sign[2] = '/';
                                            break;
                                    }
                                    return true;
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return false;
}

int main() {
    char input[15];
    while (fgets(input, sizeof(input), stdin) != NULL) {
        int len = strlen(input);
        if (len > 8) {
            printf("ERROR\n");
            continue;
        }
        int card[4] = {0};
        int nums = 0;
        for (int i = 0; i < len; i++) {
            if (input[i] >= '2' && input[i] <= '9') card[nums++] = input[i] - '0';
            else if (input[i] == '1') {
                card[nums++] = 10;
                i++;
            } else if (input[i] == 'J') card[nums++] = 11;
            else if (input[i] == 'Q') card[nums++] = 12;
            else if (input[i] == 'K') card[nums++] = 13;
            else if (input[i] == 'A') card[nums++] = 1;
        }
        if (calculate(card)) {
            char output[4][2];
            for(int i = 0; i < 4; i++) {
                if(num[i] >= 2 && num[i] <= 9) {
                    output[i][0] = num[i] + '0';
                    output[i][1] = '\0';
                } else if(num[i] == 10) {
                    strcpy(output[i], "10");
                } else if(num[i] == 11) {
                    strcpy(output[i], "J");
                } else if(num[i] == 12) {
                    strcpy(output[i], "Q");
                } else if(num[i] == 13) {
                    strcpy(output[i], "K");
                } else if(num[i] == 1) {
                    strcpy(output[i], "A");
                }
            }
            printf("%s%c%s%c%s%c%s\n", output[0], sign[0], output[1], sign[1], output[2], sign[2],
                   output[3]);
        } else {
            printf("NONE\n");
        }
    }
    return 0;
}