leetcode N-Queens

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任然是NP问题，解决此类问题主要思想就是递归，

就是用一个循环去枚举当前所有情况，然后把元素加入，递归，再把元素移除

代码1 提示 Output Limit Exceeded 输出结果中有重复的

class Solution {public:    void solveNQueensHelper(vector<vector<string> > &result, vector<string> &tempResult, vector<bool> &flagRow, vector<bool> &flagCol, int &num, int n)    {        if(num==n)        {            result.push_back(tempResult);            return ;        }                for(int i = 0; i < n; ++i)        {            if(flagRow[i]==false)                continue;            for(int j = 0; j < n; ++j)            {                if(flagCol[j]==false)                    continue;tempResult[i][j] = 'Q';flagRow[i] = false;flagCol[j] = false;num++;solveNQueensHelper(result, tempResult, flagRow, flagCol, num, n);num--;flagRow[i] = true;flagCol[j] = true;tempResult[i][j] = '.';            }        }                        return ;    } vector<vector<string> > solveNQueens(int n) {        vector<vector<string> > result;                if(n==0)            return result;                vector<bool> flagRow(n, true);        vector<bool> flagCol(n, true);        vector<string> tempResult;        for(int i = 0; i < n; ++i)        {            string str = "";            for(int j = 0; j < n; ++j)                str += '.';                            tempResult.push_back(str);        }                int num = 0;        solveNQueensHelper(result, tempResult, flagRow, flagCol, num, n);                            return result;    }};

Accepted 代码参考 http://www.cnblogs.com/TenosDoIt/p/3801621.html

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

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