377A Maze
大意: 给定棋盘, 保证初始所有白格连通, 求将$k$个白格变为黑格, 使得白格仍然连通.
$dfs$回溯时删除即可.
#include <iostream> #include <functional> #include <sstream> #include <algorithm> #include <cstdio> #include <math.h> #include <set> #include <map> #include <queue> #include <string> #include <string.h> #include <bitset> #define REP(i,a,n) for(int i=a;i<=n;++i) #define PER(i,a,n) for(int i=n;i>=a;--i) #define hr putchar(10) #define pb push_back #define lc (o<<1) #define rc (lc|1) #define mid ((l+r)>>1) #define ls lc,l,mid #define rs rc,mid+1,r #define x first #define y second #define io std::ios::sync_with_stdio(false) #define endl '\n' #define DB(a) ({REP(__i,1,n) cout<<a[__i]<<' ';hr;}) using namespace std; typedef long long ll; typedef pair<int,int> pii; const int P = 1e9+7, INF = 0x3f3f3f3f; ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;} ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;} ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;} inline int rd() {int x=0;char p=getchar();while(p<'0'||p>'9')p=getchar();while(p>='0'&&p<='9')x=x*10+p-'0',p=getchar();return x;} //head const int N = 1e3+10; int n,m,s,px,py; int vis[N][N]; char a[N][N]; const int dx[]={0,0,-1,1}; const int dy[]={-1,1,0,0}; int main() { scanf("%d%d%d", &n, &m, &s); REP(i,1,n) cin>>a[i]+1; REP(i,1,n) REP(j,1,m) if (a[i][j]=='.') px=i,py=j; function<void(int,int)> dfs = [&](int x, int y) { if (x<=0||y<=0||x>n||y>m||vis[x][y]||a[x][y]=='#') return; vis[x][y] = 1; REP(k,0,3) dfs(x+dx[k],y+dy[k]); if (s) --s,a[x][y]='X'; }; dfs(px,py); REP(i,1,n) puts(a[i]+1); }