leetcode:N-Queens 问题

一、N-QueensII

class Solution {
public:
    int totalNQueens(int n) {
        int total = 0;
        vector<int> v(n,0);
        dfs(0,n,total,v);
        return total;
    }
private:
    bool isvalide(vector<int>& v,int x){
        for(int i=0;i<x;i++){
            if(v[i]==v[x] || abs(v[x]-v[i])==abs(x - i))
                return false;
        }
        return true;
    }

    void dfs(int curr,int n,int& total,vector<int>& v){
        if(curr == n) {
            total++;
            return;
        }

        for(int i=0;i<n;i++){
            v[curr] = i;
            if(isvalide(v,curr)){
                dfs(curr+1,n,total,v);
            }
        }
    }
};

二、N-Queens

class Solution {
public:
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> result;
        vector<int> v(n,-1);
        dfs(0,n,v,result);
        return result;
    }
    bool isValide(vector<int>& v,int curr){
        for(int i=0;i< curr;i++){
            if(v[i] == v[curr] || abs(v[curr]-v[i])==abs(curr-i))
                return false;
        }
        return true;
    }
    void dfs(int curr,int n,vector<int>& v,
            vector<vector<string>>& result){
        if(curr == n){
            vector<string> temp;
            for(int i=0;i<n;i++){
                string s(n,'.');
                s[v[i]] = 'Q';
                temp.push_back(s);
            }
            result.push_back(temp);
            return;
        }
        for(int i=0;i<n;i++){
            v[curr] = i;
            if(isValide(v,curr)){
                dfs(curr+1, n, v,result);
            }
        }
    }
};