Acwing-----算法提高课第二章搜索（二）

173. 矩阵距离

• 链接：https://www.acwing.com/problem/content/175/

#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;
const int N = 1010, M = N * N;
typedef pair<int, int> PII;
#define x first
#define y second

int n, m, dist[N][N];
PII q[M];
char g[N][N];

void bfs() {
    int hh = 0, tt = -1;
    memset(dist, -1, sizeof dist);
    
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            if (g[i][j] == '1') {
                dist[i][j] = 0;
                q[++tt] = {i, j}; 
            }
        }
    }
    int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
    while (hh <= tt) {
        auto t = q[hh++];
        for (int i = 0; i < 4; ++i) {
            int a = t.x + dx[i], b = t.y + dy[i];
            if (a < 0 || a >= n || b < 0 || b >= m) continue;
            if (dist[a][b] != -1) continue;
            dist[a][b] = dist[t.x][t.y] + 1;
            q[++tt] = {a, b};
        }
    }
}

int main() {
    cin >> n >> m;
    for (int i = 0; i < n; ++i) {
        cin >> g[i];
    }
    
    bfs();
    
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cout << dist[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}

1107. 魔板

• 链接：https://www.acwing.com/problem/content/1109/

#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
#include <unordered_map>

using namespace std;
char g[2][4];
unordered_map<string, pair<char, string>> pre;
unordered_map<string, int> dist;

void set(string state) {
    for (int i = 0; i < 4; ++i)g[0][i] = state[i];
    for (int i = 7, j = 0; j < 4; --i, ++j) g[1][j] = state[i];
}

string get() {
    string ans;
    for (int i = 0; i < 4; ++i) ans += g[0][i];
    for (int i = 3; i >= 0; --i) ans += g[1][i];
    return ans;
}

string move0(string state) {
    set(state);
    for (int i = 0; i < 4; ++i) swap(g[0][i], g[1][i]);
    return get();
}

string move1(string state) {
    set(state);
    int v0 = g[0][3], v1 = g[1][3];
    for (int i = 3; i >= 0; --i) {
        g[0][i] = g[0][i - 1];
        g[1][i] = g[1][i - 1];
    }
    g[0][0] = v0, g[1][0] = v1;
    return get();
}

string move2(string state) {
    set(state);
    int v = g[0][1];
    g[0][1] = g[1][1];
    g[1][1] = g[1][2];
    g[1][2] = g[0][2];
    g[0][2] = v;
    return get();
}

int bfs(string start, string end) {
    if (start == end) return 0;
    queue<string> q;
    q.push(start);
    dist[start] = 0;
    
    while (!q.empty()) {
        auto t = q.front();
        q.pop();
        
        string m[3];
        m[0] = move0(t);
        m[1] = move1(t);
        m[2] = move2(t);
        
        for (int i = 0; i < 3; ++i) {
            if (!dist.count(m[i])) {
                dist[m[i]] = dist[t] + 1;
                pre[m[i]] = {'A' + i, t};
                q.push(m[i]);
                if (m[i] == end) return dist[end];
            }
        }
    }
    return -1;
}

int main() {
    int x;
    string start, end;
    for (int i = 0; i < 8; ++i) {
        cin >> x;
        end += char(x + '0');
    }
    
    for (int i = 1; i <= 8; ++i) start += char('0' + i);
    int step = bfs(start, end);
    
    cout << step << endl;
    
    string ans;
    while (end != start) {
        ans += pre[end].first;
        end = pre[end].second;
    }
    reverse(ans.begin(), ans.end());
    if (step > 0) cout << ans << endl;
    return 0;
}

175. 电路维修

• 链接：https://www.acwing.com/problem/content/177/

#include <cstring>
#include <algorithm>
#include <deque>
#include <iostream>

using namespace std;
const int N = 510, M = N * N;
#define x first
#define y second

typedef pair<int, int> PII;
int n, m;
char g[N][N];
PII q[M];
int dist[N][N];
bool st[N][N];

int bfs() {
    deque<PII> q;
    q.push_back({0, 0});
    memset(dist, 0x3f, sizeof dist);
    memset(st, false, sizeof st);
    
    dist[0][0] = 0;
    int dx[4] = {-1, -1, 1, 1}, dy[4] = {-1, 1, 1, -1};
    int ix[4] = {-1, -1, 0, 0}, iy[4] = {-1, 0, 0, -1};
    char cs[5] = "\\/\\/";
    
    while (q.size()) {
        auto t = q.front();
        q.pop_front();
        
        int x = t.x, y = t.y;
        
        if (x == n && y == m) return dist[x][y];
        
        if (st[x][y]) continue;
        st[x][y] = true;
        
        for (int i = 0; i < 4; ++i) {
            int a = x + dx[i], b = y + dy[i];
            if (a < 0 || a > n || b < 0 || b > m) continue;
            int ga = x + ix[i], gb = y + iy[i];
            int w = g[ga][gb] != cs[i];
            int d = dist[x][y] + w;
            
            if (d <= dist[a][b]) {
                dist[a][b] = d;
                if (!w) q.push_front({a, b});
                else q.push_back({a, b});
            }
        }
    }
    return -1;
}

int main() {
    int T;
    cin >> T;
    while (T--) {
        cin >> n >> m;
        for (int i = 0; i < n; ++i) cin >> g[i];
         
        if (n + m & 1) puts("NO SOLUTION");
        else cout << bfs() << endl;
    }
    return 0;
}