使用深搜

# include <bits/stdc++.h>
using namespace std;
char a[200][2];
void dfs(char begin) {
	if (begin == '*') {
		return;
	}
	printf("%c", begin);
	dfs(a[begin][0]);
	dfs(a[begin][1]);
}
int main() {
	int n;
	scanf("%d", &n);
	char c;
	for (int i = 0; i < n; i++) {
		char s[5];
		scanf("%s", &s);
		if (i == 0) {
			c = s[0];
		}
		int index = s[0];
		a[index][0] = s[1];
		a[index][1] = s[2];
	}
	dfs(c);
	return 0;
}