# HackerRank World CodeSprint 12: Red Knight's Shortest Path

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https://www.hackerrank.com/contests/world-codesprint-12/challenges/red-knights-shortest-path

## implementation

#include <climits>
#include <cstdio>
#include <queue>
#include <tuple>
#include <vector>
#define REP(i, n) for (int i = 0; (i) < int(n); ++ (i))
using namespace std;

const int dy[] = { -2, -2, 0, 2, 2, 0 };
const int dx[] = { -1, 1, 2, 1, -1, -2 };
const char *name[] = { "UL", "UR", "R", "LR", "LL", "L" };
int main() {
// input
int n, y0, x0, y1, x1; scanf("%d%d%d%d%d", &n, &y0, &x0, &y1, &x1);
// solve
// // dp
vector<vector<int> > dp(n, vector<int>(n, INT_MAX));
queue<pair<int, int> > que;
dp[y1][x1] = 0;
que.emplace(y1, x1);
while (not que.empty()) {
int y, x; tie(y, x) = que.front(); que.pop();
REP (i, 6) {
int ny = y + dy[i];
int nx = x + dx[i];
if (0 <= ny and ny < n and 0 <= nx and nx < n) {
if (dp[ny][nx] == INT_MAX) {
dp[ny][nx] = dp[y][x] + 1;
que.emplace(ny, nx);
}
}
}
}
if (dp[y0][x0] == INT_MAX) {
printf("Impossible\n");
return 0;
}
// // construct
vector<char const *> result;
for (int y = y0, x = x0; dp[y][x]; ) {
REP (i, 6) {
int ny = y + dy[i];
int nx = x + dx[i];
if (0 <= ny and ny < n and 0 <= nx and nx < n) {
if (dp[ny][nx] < dp[y][x]) {
y = ny;
x = nx;
result.push_back(name[i]);
break;
}
}
}
}
// output
int dist = result.size();
printf("%d\n", dist);
REP (i, dist) {
printf("%s%c", result[i], i < dist - 1 ? ' ' : '\n');
}
return 0;
}