纯模拟

# include <bits/stdc++.h>
using namespace std;
string s1, s2;
int main() {
	cin >> s1 >> s2;
	int xa = s1[0] - 'a' + 1;
	int ya = s1[1] - '0';
	int xb = s2[0] - 'a' + 1;
	int yb = s2[1] - '0';
	int n = max(abs(xa - xb), abs(ya - yb));
	printf("%d\n", n);
	while (n--) {
		if (xa > xb && ya > yb) {
			xa--;
			ya--;
			printf("LD\n");
			continue;
		}
		if (xa > xb && ya == yb) {
			xa--;
			printf("L\n");
			continue;
		}
		if (xa > xb && ya < yb) {
			xa--;
			ya++;
			printf("LU\n");
			continue;
		}
		if (xa == xb && ya > yb) {
			ya--;
			printf("D\n");
			continue;
		}
		if (xa == xb && ya < yb) {
			ya++;
			printf("U\n");
			continue;
		}
		if (xa < xb && ya > yb) {
			xa++;
			ya--;
			printf("RD\n");
			continue;
		}
		if (xa < xb && ya == yb) {
			xa++;
			printf("R\n");
			continue;
		}
		if (xa < xb && ya < yb) {
			xa++;
			ya++;
			printf("RU\n");
			continue;
		}
	}
}