[이취코] 유형별 알고리즘 - DFS/BFS(C++)

1. 특정 거리의 도시 찾기

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

#define MAX 300001
int n, m, k, x;
int i, j;
vector<int> arr[MAX];
vector<int> d(MAX, -1);

void bfs(int start) {
    d[start] = 0;
    queue<int> q;
    q.push(start);

    while (!q.empty()) {
        int now = q.front();
        q.pop();

        for (auto &i: arr[now]) {
            if (d[i] == -1) { //방문 안했으면
                d[i] = d[now] + 1;
                q.push(i);
            }
        }
    }
}

int main() {
    cin >> n >> m >> k >> x;

    for (int z = 0; z < n; z++) {
        cin >> i >> j;
        arr[i].push_back(j);
    }
    bfs(x);

    bool isTrue = false;
    for (int z = 1; z <= n; z++) {
        if (d[z] == k) {
            cout << z << "\n";
            isTrue = true;
        }
    }
    if (!isTrue)
        cout << -1 << "\n";
    return 0;
}

 

2. 연구소

#include <iostream>
#include <vector>
using namespace std;

#define MAX 11
int arr[MAX][MAX];
int tmp[MAX][MAX];
int n, m;
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
int result = 0;

void virus(int x, int y) { //dfs
    for (int i = 0; i < 4; i++) {
        int nx = x + dx[i];
        int ny = y + dy[i];

        if (nx < 0 || nx > n || ny < 0 || ny > m)
            continue;
        if (tmp[nx][ny] == 0) {
            tmp[nx][ny] = 2;
            virus(nx, ny);
        }
    }
}

int getScore() {
    int cnt = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (tmp[i][j] == 0) {
                cnt++;
            }
        }
    }
    return cnt;
}

void dfs(int cnt) { //dfs로 벽 설치
    if (cnt == 3) {
        //바이러스 퍼뜨리기
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                tmp[i][j] = arr[i][j];
            }
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (tmp[i][j] == 2)
                    virus(i, j);
            }
        }

        //안전영역 최대인 것으로 교체
        result = max(result, getScore());
        return;
    }

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (arr[i][j] == 0) {
                arr[i][j] = 1;
                cnt++;
                dfs(cnt);
                arr[i][j] = 0;
                cnt--;
            }
        }
    }
}

int main() {
    cin >> n >> m;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> arr[i][j];
        }
    }
    dfs(0);
    cout << result;
    return 0;
}

 

3. 경쟁적 전염

vector 넣고 for(auto i: virus) 돌려서 계속 런타임 에러 떴다 ..^^~

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define MAX 201
int n, k, s, x, y;
int arr[MAX][MAX];
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> k;
    vector<pair<int, pair<int, int> >> virus;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> arr[i][j];
            if (arr[i][j] != 0)
                virus.push_back({arr[i][j], {i, j}});
        }
    }
    cin >> s >> x >> y;
    sort(virus.begin(), virus.end());

    int cur = 1;
    while (cur <= s) {
        int size = virus.size();
        for (int i = 0; i < size; i++) {
            int curVirus = virus[i].first;
            int curx = virus[i].second.first;
            int cury = virus[i].second.second;

            for (int i = 0; i < 4; i++) {
                int nx = curx + dx[i];
                int ny = cury + dy[i];

                if (nx < 0 || nx >= n || ny < 0 || ny >= n)
                    continue;
                if (arr[nx][ny] > 0)
                    continue;
                arr[nx][ny] = curVirus;
                virus.push_back({curVirus, {nx, ny}});
            }
        }

        if (arr[x - 1][y - 1] > 0)
            break;
        cur++;
    }

    cout << arr[x - 1][y - 1];
    return 0;
}

 

4. 연산자 끼워넣기

#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;

int main() {
    int n, num;
    vector<int> v, op; //숫자들, 연산자 수
    int minNum = 1000000000, maxNum = -1000000000;

    cin >> n;
    while (n--) {
        cin >> num;
        v.push_back(num);
    }
    for (int i = 0; i < 4; i++) {
        cin >> num;
        for (int j = 0; j < num; j++) {
            op.push_back(i);
        }
    }

    do {
        int sum = v[0];
        for (int i = 0; i < v.size() - 1; i++) {
            switch (op[i]) {
                case 0: // +
                    sum += v[i + 1];
                    break;
                case 1: // -
                    sum -= v[i + 1];
                    break;
                case 2: // *
                    sum *= v[i + 1];
                    break;
                case 3: // /
                    sum /= v[i + 1];
                    break;
            }
        }

        if (sum < minNum) { //최솟값
            minNum = sum;
        }
        if (sum > maxNum) { //최댓값
            maxNum = sum;
        }

    } while (next_permutation(op.begin(), op.end()));

    cout << maxNum << "\n" << minNum;
    return 0;
}