[leetcode刷题系列]N-Queens

class Solution {
const static int MAXN = 100;
bool col[MAXN], add[MAXN], minus[MAXN];
int ans[MAXN];
void dfs(int now, int n, vector<vector<string> >& ret){
if(now >= n){
vector<string> vs;
for(int i = 0; i < n; ++ i){
string s = "";
for(int j = 0; j < n; ++ j)
if(j == ans[i])
s += 'Q';
else
s += '.';
vs.push_back(s);
}
ret.push_back(vs);
return ;
}
for(int i = 0; i < n; ++ i){
if(!col[i] && !add[now + i] && !minus[now - i + n]){
col[i] = true;
add[now + i] = true;
minus[now - i + n] = true;
ans[now] = i;
dfs(now + 1, n, ret);
col[i] = false;
add[now + i] = false;
minus[now - i + n] = false;
}
}
}
public:
vector<vector<string> > solveNQueens(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
memset(col, 0x00, sizeof(col));
memset(add, 0x00, sizeof(add));
memset(minus, 0x00, sizeof(minus));
vector<vector<string> > ret;
dfs(0, n, ret);
return ret;
}
};