I am working on Leetcode problem https://leetcode.com/problems/sliding-puzzle/
class Solution {
public:
int slidingPuzzle(vector<vector<int>>& board) {
int res = 0;
set<vector<vector<int>>> visited;
queue<pair<vector<vector<int>>, vector<int>>> q;
vector<vector<int>> correct{{1, 2, 3}, {4, 5, 0}};
vector<vector<int>> dirs{{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < 3; ++j) {
if (board[i][j] == 0) q.push({board, {i, j}});
}
}
while (!q.empty()) {
for (int i = q.size() - 1; i >= 0; --i) {
vector<vector<int>> t = q.front().first;
auto zero = q.front().second; q.pop();
if (t == correct) return res;
visited.insert(t);
for (auto dir : dirs)
{
int x = zero[0] + dir[0], y = zero[1] + dir[1];
if (x < 0 || x >= 2 || y < 0 || y >= 3) continue;
/* option1
vector<vector<int>> cand = t;
swap(cand[zero[0]][zero[1]], cand[x][y]);
if (visited.count(cand)) continue;
q.push({cand, {x, y}});
*/
/* option2
swap(t[zero[0]][zero[1]], t[x][y]);
if (visited.count(t)) continue;
q.push({t, {x, y}});
swap(t[zero[0]][zero[1]], t[x][y]);
*/
}
}
++res;
}
return -1;
}
};
if I keep option1 remove option2 it works,
however when I keep option2 remove option1 it doesn't work!
But these two code block should work the same. I have been trying to figure it out for a couple of hours. So frustrated and no clue
The Bug is in here if (visited.count(t)) continue;
basically, when visited.count(t) is true
you will not undo the swap.