计算123456789，所有3位数加法的组合。看了Milo Yip大神的知乎答案，赶忙来补充一下他的，以前写的可真烂。

another_plus_puzzle.c

#include <stdio.h>

static int num_ten[] = {
    1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 100000000
};

int get_num(n, s, e) {
    int d = num_ten[9 - e];
    int r = num_ten[e - s + 1];
    return n / d % r;
}

void puzzle_1(int n) {
    // abc + def = ghi
    int abc = get_num(n, 1, 3);
    int def = get_num(n, 4, 6);
    int ghi = get_num(n, 7, 9);
    if (abc + def == ghi) {
        printf("%d + %d = %d\n", abc, def, ghi);
    }
}

void puzzle_2(int n) {
    // ab - cd = ef = g * hi
    int ab = get_num(n, 1, 2);
    int cd = get_num(n, 3, 4);
    int ef = get_num(n, 5, 6);
    int g = get_num(n, 7, 7);
    int hi = get_num(n, 8, 9);
    if (ab - cd == ef && ef == g * hi) {
        printf("%d - %d = %d = %d * %d\n", ab, cd, ef, g, hi);
    }
}

void puzzle_3(int n) {
    // abc:def:ghi = 1:2:3
    int abc = get_num(n, 1, 3);
    int def = get_num(n, 4, 6);
    int ghi = get_num(n, 7, 9);    
    if (abc * 2 == def && abc * 3 == ghi) {
        printf("%d:%d:%d\n", abc, def, ghi);
    }    
}

void f(int i, int m, int r, void (*output)(int)) {
    if (i == 0) {
        output(r);
    }
    else {
        for (int j = 1; j < 10; j++) {
            if (((1 << j) & m) == 0) {
                f(i - 1, m | (1 << j), r * 10 + j, output);
            }
        }
    }
}


int main() {
    f(9, 1, 0, puzzle_1);
    return 0;
}

plus_puzzle.c

#include <stdio.h>
#include <time.h>

struct result 
{
    int _100a, _100b, _100c;
    int _10a, _10b, _10c;
    int _a, _b, _c;
};

inline int check_num(char *nums, int value)
{
    return nums[value] != '0';
}
inline void take_num(char *nums, int value)
{
    nums[value] = '0';
}

inline void set_num(char *nums, int value)
{
    nums[value] = value;
}

inline int check_value(struct result *r)
{
    int a = r->_100a * 100 + r->_10a * 10 + r->_a;
    int b = r->_100b * 100 + r->_10b * 10 + r->_b;
    int c = r->_100c * 100 + r->_10c * 10 + r->_c; 
    /*return a < b && a + b == c;*/
    return a + b == c;
}

int count = 0;

void check_exp(char *nums, int add, struct result *r, int level)
{
    int i = 1;

    for(; i < 10; i++) {

        int j = 1;
        if (check_num(nums, i)) {
            for(; j < 10; j++) {
                /*if (j == i) continue;*/
                if (j == i) continue;
                if (level == 1) {
                    if (j > i) continue;
                    if (j + i > 9) continue;
                }

                int k = 1;
                if (check_num(nums, j)) {
                    for(; k < 10; k++) {
                        if (k == j || k == i) continue;

                        if (check_num(nums, k)) {
                            int addten = add == 1 ? 10 : 0;

                            int plus = 0;
                            int ok = 0;
                            if (i + j == k + addten) {
                                ok = 1;
                            }
                            else if (i + j == k - 1 + addten) {
                                ok = level != 3;
                                plus = 1;
                            }

                            if (ok) {
                                take_num(nums, i);
                                take_num(nums, j);
                                take_num(nums, k);

                                switch(level) {
                                    case 1:
                                        r->_100a = i;
                                        r->_100b = j;
                                        r->_100c = k;
                                        check_exp(nums, plus, r, level + 1);
                                        break;

                                    case 2:
                                        r->_10a = i;
                                        r->_10b = j;
                                        r->_10c = k;
                                        check_exp(nums, plus, r, level + 1);
                                        break;

                                    case 3:
                                        r->_a = i;
                                        r->_b = j;
                                        r->_c = k;

                                        /*if (check_value(r)) {*/
                                            ++count;
                                            /*printf("result:%d%d%d + %d%d%d = %d%d%d\n", r->_100a, r->_10a, r->_a, r->_100b, r->_10b, r->_b, r->_100c, r->_10c, r->_c);*/
                                        /*}*/
                                        break;
                                }

                                // return flag
                                set_num(nums, i);
                                set_num(nums, j);
                                set_num(nums, k);
                            }
                        }
                    }
                }
            }
        }
    }
}


int main()
{

    clock_t start, end;
    char nums[] = "0123456789";
    struct result r;

    int times = 1000;

    start = clock();
    while(times--) {
        check_exp(nums, 0, &r, 1);
    }
    end = clock();

    printf("count:%d, use time:%lu\n", count, end - start);

    return 0;
}

你把plus_puzzle改为plus_puzzle.c，就能有语法高亮了……

果然。。。