POJ4007.Flood-it!

Posted 2020-11-02 sigongzi

原题戳这里

题解

搜索是个好东西，不是人人都会搜

迭代加深，然后用一个函数估值，值是除了和左上连通的部分还有几个颜色不同的块，如果走的步数加上估值大于当前枚举的深度就跳出

代码

#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <ctime>
#define MAXN 200005
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
int N,a[10][10],D,vis[10][10],_vis[10][10];
int dx[4] = {0,1,0,-1};
int dy[4] = {1,0,-1,0};
void pre(int x,int y) {
    vis[x][y] = 1;
    for(int i = 0 ; i <= 3 ; ++i) {
        if(vis[x + dx[i]][y + dy[i]]) continue;
        if(a[x + dx[i]][y + dy[i]] == a[x][y]) {
            pre(x + dx[i],y + dy[i]);
        }
    }
}
bool expend(int x,int y,int c) {
    _vis[x][y] = 1;
    bool flag = 0;
    if(!vis[x][y]) flag = 1;
    for(int i = 0 ; i <= 3 ; ++i) {
        if(_vis[x + dx[i]][y + dy[i]]) continue;
        if(vis[x + dx[i]][y + dy[i]] || a[x + dx[i]][y + dy[i]] == c) 
            flag = expend(x + dx[i],y + dy[i],c) || flag;
    }
    return flag;
}
int calc() {
    bool used[6];memset(used,0,sizeof(used));
    for(int i = 1 ; i <= N ; ++i) {
        for(int j = 1 ; j <= N ; ++j) {
            if(!vis[i][j]) {
                used[a[i][j]] = 1;
            }
        } 
    }
    int res = 0;
    for(int i = 0 ; i <= 5 ; ++i) res += used[i];
    return res;
}
bool dfs(int dep) {
    if(dep > D) {
        if(calc() == 0) return 1;
        else return 0;
    }
    if(dep + calc() - 1 > D) return false;
    for(int i = 0 ; i <= 5 ; ++i) {
        memset(_vis,0,sizeof(_vis));
        if(!expend(1,1,i)) continue;
        int cpy[10][10];
        memcpy(cpy,vis,sizeof(vis));
        memcpy(vis,_vis,sizeof(vis));
        if(dfs(dep + 1)) return 1;
        memcpy(vis,cpy,sizeof(cpy));
    }
    return false;
}
void Solve() {
    bool used[6];
    memset(used,0,sizeof(used));
    for(int i = 1 ; i <= N ; ++i) {
        for(int j = 1 ; j <= N ; ++j) {
            scanf("%d",&a[i][j]);
            used[a[i][j]] = 1;
        }
    }
    for(int i = 0 ; i <= N + 1; ++i) {
        a[0][i] = a[N + 1][i] = 6;
        a[i][0] = a[i][N + 1] = 6;
    }
    memset(vis,0,sizeof(vis));
    pre(1,1);
    if(calc() == 0) {puts("0");return;}
    for(int dep = calc(); ; ++dep) {
        D = dep;
        if(dfs(1)) {
            printf("%d\n",dep);
            return;
        } 
    }
}

int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    while(scanf("%d",&N)!=EOF && N) {
        if(N == 0) break;
        Solve();
    }
    return 0;
}