文章目录 【LC刷题】DAY22：491 46 47 332 51 37 491. 非递减子序列 [link](https://leetcode.cn/problems/non-decreasing-subsequences/description/) 46. 全排列 [link](https://leetcode.cn/problems/permutations/description/) 332. 重新安排行程 [link](https://leetcode.cn/problems/reconstruct-itinerary/description/) 51. N 皇后 [link](https://leetcode.cn/problems/n-queens/description/) 37. 解数独 [link](https://leetcode.cn/problems/sudoku-solver/description/)
491. 非递减子序列 link
class Solution {
public:vector<vector<int>> result;vector<int> path;void backtracking(vector<int>& nums, int startIndex){if(path.size() > 1){result.push_back(path);}unordered_set<int> uset;for(int i = startIndex; i < nums.size(); i ++){if ((!path.empty() && nums[i] < path.back())|| uset.find(nums[i]) != uset.end()) {continue;}uset.insert(nums[i]);path.push_back(nums[i]);backtracking(nums, i + 1);path.pop_back();}}vector<vector<int>> findSubsequences(vector<int>& nums) {backtracking(nums, 0);return result;}
};
class Solution {
public:vector<vector<int>> result;vector<int> path;void backtracking(vector<int>& nums, vector<bool> used){if(path.size() == nums.size()){result.push_back(path);return;}for(int i = 0; i < nums.size(); i ++){if(used[i] == true) continue;used[i] = true;path.push_back(nums[i]);backtracking(nums, used);path.pop_back();used[i] = false;}}vector<vector<int>> permute(vector<int>& nums) {vector<bool> used(nums.size(), false);backtracking(nums, used);return result;}
};
332. 重新安排行程 link
class Solution {
public:unordered_map<string,map<string, int>> targets;bool backtracking(int ticketNum, vector<string>& result){if(result.size() == ticketNum + 1){return true;}for(pair<const string, int>& target :targets[result[result.size() - 1]]){if(target.second > 0){result.push_back(target.first);target.second --;if(backtracking(ticketNum, result)) return true;result.pop_back();target.second++;}}return false;}vector<string> findItinerary(vector<vector<string>>& tickets) {vector<string> result;for(const vector<string>& vec:tickets){targets[vec[0]][vec[1]] ++;}result.push_back("JFK");backtracking(tickets.size(), result);return result;}
};
51. N 皇后 link
class Solution {
public:vector<vector<string>> result;void backtracking(int n, int row, vector<string> &chessboard) {if (row == n) {result.push_back(chessboard);return;}for (int col = 0; col < n; col++) {if (isvalid(row, col, chessboard, n)) {chessboard[row][col] = 'Q';backtracking(n, row + 1, chessboard);chessboard[row][col] = '.';}}}bool isvalid(int row, int col, vector<string> &chessboard, int n) {// 检查列for (int i = 0; i < row; i++) {if (chessboard[i][col] == 'Q') {return false;}}// 检查左上到右下的对角线for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {if (chessboard[i][j] == 'Q') {return false;}}// 检查右上到左下的对角线for (int i = row - 1, j = col + 1; i >= 0 && j < n; i--, j++) {if (chessboard[i][j] == 'Q') {return false;}}// 检查水平方向的对角线for (int i = row - 1, k = 1; i >= 0 && col + k < n; i--, k++) {if (chessboard[i][col + k] == 'Q') {return false;}}for (int i = row - 1, k = 1; i >= 0 && col - k >= 0; i--, k++) {if (chessboard[i][col - k] == 'Q') {return false;}}return true;}vector<vector<string>> solveNQueens(int n) {vector<string> chessboard(n, string(n, '.'));backtracking(n, 0, chessboard);return result;}
};
class Solution {
public:bool backtracking(vector<vector<char>>& board){for(int i = 0; i < board.size(); i ++){for(int j = 0; j < board[0].size(); j ++){if(board[i][j] != '.') continue ;for(char k = '1'; k <= '9'; k ++){if(isvalid(i, j, k, board)){board[i][j] = k;if(backtracking(board)) return true;board[i][j] = '.';}}return false;}}return true;}bool isvalid(int row, int col, char val, vector<vector<char>>& board){for(int i = 0; i< 9; i ++){if(board[row][i] == val){return false;}}for(int j = 0; j < 9; j ++){if(board[j][col] == val){return false;}}int startRow = (row / 3) * 3;int startCol = (col / 3) * 3;for(int i = startRow; i < startRow + 3; i ++){for(int j = startCol; j < startCol+3; j ++){if(board[i][j] == val){return false;}}}return true;}void solveSudoku(vector<vector<char>>& board) {backtracking(board);}
};
