算法训练Day26 | 332.重新安排行程 ● 51. N皇后 ● 37. 解数独

332.重新安排行程

class Solution {
public:
    vector<string> result;
    bool backtracking(vector<vector<string>>& tickets, vector<bool>& used){
        if(result.size()==tickets.size()+1){
            return true;
        }
        for(int i=0; i<tickets.size(); i++){
            if(used[i] == true){
                continue;
            }
            if(tickets[i][0]==result.back()){
                result.push_back(tickets[i][1]);
                used[i] = true;
                if(backtracking(tickets, used)) return true;
                result.pop_back();
                used[i] = false;
            }
        }
        return false;

    }
    vector<string> findItinerary(vector<vector<string>>& tickets) {
        result.push_back("JFK");

        vector<bool> used(tickets.size(), false);
        backtracking(tickets, used);
        return result;

    }
};

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参考文章：代码随想录-332.重新安排行程

51. N皇后

class Solution {
public:
    vector<vector<string>> result;
    bool isValid(int col, int row, vector<string>& temp, int n){
        for(int i=0; i<row; i++){
            if(temp[i][col]=='Q') return false;
        }
        for(int i=row-1, j=col-1; i>=0&&j>=0; i--, j--){
            if(temp[i][j]=='Q') return false;
        }
        for(int i=row-1, j=col+1; i>=0&&j<n; i--, j++){
            if(temp[i][j]=='Q') return false;
        }
        return true;
    }
    void backtracking(int n, int row, vector<string>& temp){
        if(row == n){
            result.push_back(temp);
            return;
        }
        for(int i=0; i<n; i++){
            if(isValid(i, row, temp, n)){
                temp[row][i] = 'Q';
                backtracking(n, row+1, temp);
                temp[row][i] = '.';
            }
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        result.clear();
        vector<string> temp(n, string(n, '.'));
        backtracking(n,0, temp);
        return result;

    }
};
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参考文章：代码随想录- 51. N皇后

37. 解数独

class Solution {
public:
    bool isValid(int row, int col, char val, vector<vector<char>>& board){
        for(int i=0; i<board.size(); i++){
            if(board[i][col]==val){
                return false;
            }
        }
        for(int j=0; j<board.size(); j++){
            if(board[row][j]==val){
                return false;
            }
        }
        int row_s = (row/3)*3;
        int col_s = (col/3)*3;
        for(int i = row_s; i<row_s+3; i++){
            for(int j=col_s; j<col_s+3; j++){
                if(board[i][j]==val){
                    return false;
            }
            }
        }
        return true;
    }
    bool backtracking(vector<vector<char>>& board){
        for(int i=0; i<board.size(); i++){
            for(int j=0; j<board.size(); j++){
                if(board[i][j] == '.'){
                    for(char val='1'; val<='9'; val++){
                        if(isValid(i,j,val, board)){
                            board[i][j]=val;
                            if(backtracking(board)) return true;
                            board[i][j]='.';
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
    void solveSudoku(vector<vector<char>>& board) {
        backtracking(board);
    }
};

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参考文章：代码随想录- 37. 解数独