LeetCode 332.重新安排行程

题目链接：

LeetCode 332.重新安排行程

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 ) { // 记录到达机场是否飞过了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]]++; // 记录映射关系}result.push_back("JFK"); // 起始机场backtracking(tickets.size(), result);return result;}
};

LeetCode 51.N皇后

题目链接：

LeetCode 51.N皇后

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) {vector<string>chessboard(n,string(n,'.'));backtracking(n,0,chessboard);return result;}
};

LeetCode 37.解数独

题目链接：

LeetCode 37.解数独

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++) { // (i, j) 这个位置放k是否合适if (isValid(i, j, k, board)) {board[i][j] = k; // 放置kif (backtracking(board))return true; // 如果找到合适一组立刻返回board[i][j] = '.'; // 回溯，撤销k}}return false; // 9个数都试完了，都不行，那么就返回false}}}return true;}bool isValid(int row, int col, char val, vector<vector<char>>& board) {for (int i = 0; i < 9; i++) { // 判断行里是否重复if (board[row][i] == val) {return false;}}for (int j = 0; j < 9; j++) { // 判断列里是否重复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++) { // 判断9方格里是否重复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); }
};