代码随想录算法训练营第三十天|332.重新安排行程、51. N皇后、37. 解数独

332.重新安排行程

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台
文档讲解：代码随想录

C++代码：

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) {targets.clear();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

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台
文档讲解：代码随想录
视频讲解：这就是传说中的N皇后？回溯算法安排！| LeetCode：51.N皇后_哔哩哔哩_bilibili

C++代码：

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) {for (int i = 0; i < row; i++) {if (chessboard[i][col] == 'Q') {return false;}}for (int i = row - 1, j = col - 1; i >=0 && j >= 0; i--, j--) {if (chessboard[i][j] == 'Q') {return false;}}for(int i = row - 1, j = col + 1; i >= 0 && j < n; i--, j++) {if (chessboard[i][j] == 'Q') {return false;}}return true;}vector<vector<string>> solveNQueens(int n) {result.clear();std::vector<std::string> chessboard(n, std::string(n, '.'));backtracking(n, 0, chessboard);return result;}
};

37. 解数独

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台
文档讲解：代码随想录
视频讲解：回溯算法二维递归？解数独不过如此！| LeetCode：37. 解数独_哔哩哔哩_bilibili

C++代码：

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] == '.') {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);}
};