FDCAJHxIBCFEH=FBAECIIJEGIH

main.c

// https://twitter.com/miharasan/status/1348654370921934849?s=20

#include <stdio.h>

long v[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

long val(char alpha) {
	return v[alpha - 'A'];
}

long vals(char *text) {
	long res = 0;
	for (int i = 0; text[i] != '\0'; ++i) {
		res = res * 10 + val(text[i]);
	}
	return res;
}

void iterate(int o) {
	if (o == 0) {
		long v1 = vals("FDCAJH");
		long v2 = vals("IBCFEH");
		long v3 = vals("FBAECIIJEGIH");
		if (v1 * v2 == v3) {
			printf("%ld*%ld=%ld\n", v1, v2, v3);
		}
	} else {
		long ov = v[o - 1];
		for (int i = 0; i < o; ++i) {
			long nv = v[i];
			v[i] = ov;
			v[o - 1] = nv;
			iterate(o - 1);
			v[i] = nv;
			v[o - 1] = ov;
		}
	}
}

int main(void) {
	iterate(10);
	return 0;
}