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+// 773. Sliding Puzzle
+#include "leetcode.h"
+
+/*
+ * on an empty 2 x 3 board there are five tiles labeled from 1 to 5 and an empty
+ * square represented by 0. a move consists of choosing 0 and a 4-directionall
+ * adjacent number and swapping it. the state of the board is solved if and only
+ * if the board is '[[1,2,3],[4,5,0]]'. given the puzzle 'board', return the
+ * least number of moves required so that the state of the board is solved. if
+ * it is impossible for the state of the board to be solved, return -1
+ */
+
+class Solution {
+public:
+ int slidingPuzzle(vector<vector<int>> &board) {
+ string begin = "", end = "123450";
+ vector<vector<int>> moves = {{1, 3}, {0, 2, 4}, {1, 5},
+ {0, 4}, {1, 3, 5}, {2, 4}};
+ for (int i = 0; i < board.size(); i++)
+ for (int j = 0; j < board[0].size(); j++)
+ begin += to_string(board[i][j]);
+ unordered_set<string> vis;
+ vis.insert(begin);
+ queue<pair<string, int>> qp;
+ qp.push({begin, 0});
+ while (!qp.empty()) {
+ auto p = qp.front();
+ qp.pop();
+ string curr = p.first;
+ int dist = p.second, idx = curr.find("0");
+ if (curr == end)
+ return dist;
+ for (auto &i : moves[idx]) {
+ string next = curr;
+ swap(next[idx], next[i]);
+ if (!vis.count(next)) {
+ vis.insert(next);
+ qp.push({next, dist + 1});
+ }
+ }
+ }
+ return -1;
+ }
+};
+
+int main() {
+ Solution obj;
+ vvd b1 = {{1, 2, 3}, {4, 0, 5}}, b2 = {{1, 2, 3}, {5, 4, 0}},
+ b3 = {{4, 1, 2}, {5, 0, 3}};
+ printf("%d\n", obj.slidingPuzzle(b1)); // expect 1
+ printf("%d\n", obj.slidingPuzzle(b2)); // expect -1
+ printf("%d\n", obj.slidingPuzzle(b3)); // expect 5
+}