代码随想录 101. 孤岛的总面积

101. 孤岛的总面积

#include<bits/stdc++.h>
using namespace std;
 
int dfs(vector<vector<int>>& mp, vector<vector<int>>& visit, int y, int x, int s, int& notEdge){
    if (mp[y][x] == 0 || visit[y][x] == 1) return s * notEdge;
    if (mp[y][x] == 1 && visit[y][x] == 0){
        s++;
        visit[y][x] = 1;
    }
    if (y == 0 || y == mp.size() - 1 || x == 0 || x == mp[0].size() - 1) notEdge = 0;
    if (y > 0) s = dfs(mp, visit, y - 1, x, s, notEdge);
    if (x > 0) s = dfs(mp, visit, y, x - 1, s, notEdge);
    if (y < mp.size() - 1) s = dfs(mp, visit, y + 1, x, s, notEdge);
    if (x < mp[0].size() - 1) s = dfs(mp, visit, y, x + 1, s, notEdge);
    return s * notEdge;
}
 
int main(){
    int n, m;
    cin >> n >> m;
    int result = 0;
    vector<vector<int>> mp(n, vector<int>(m, 0));
    vector<vector<int>> visit(n, vector<int>(m, 0));
    for (int i = 0; i < n; i++){
        for (int j = 0; j < m; j++){
            cin >> mp[i][j];
        }
    }
    int isEdge;
    for (int i = 0; i < mp.size(); i++){
        for (int j = 0; j < mp[0].size(); j++){
            if (mp[i][j] == 1 && visit[i][j] == 0){
                isEdge = 1;
                result += dfs(mp, visit, i, j, 0, isEdge);
            }
        }
    }
    cout << result;
    return 0;
}

dfs版本，在之前求总面积的基础上增加了判断是否有有边缘位置元素的部分，所以增加了一个notEdge变量，在遇到边缘元素时标记为0，以使所有输出均变为0，此外需要注意，即使遇到了边缘元素也需要先将所有陆地遍历并在visit上标记。毕竟做人需要有始有终）

#include<bits/stdc++.h>
using namespace std;

int bfs(vector<vector<int>>& mp, vector<vector<int>>& visit, int y, int x){
    int result = 0;
    int notEdge = 1;
    queue<pair<int, int>> q;
    q.push({y, x});
    visit[y][x] = 1;
    result++;
    while(!q.empty()){
        pair<int, int> tmp = q.front();
        q.pop();
        int tmpy = tmp.first, tmpx = tmp.second;
        if (tmpy == 0 || tmpx == 0 || tmpy == mp.size() - 1 || tmpx == mp[0].size() - 1) notEdge = 0;
        
        if (tmpy > 0){
            if (mp[tmpy - 1][tmpx] == 1 && visit[tmpy - 1][tmpx] == 0){
                q.push({tmpy - 1, tmpx});
                visit[tmpy - 1][tmpx] = 1;
                result++;
            }
        }
        if (tmpx > 0){
            if (mp[tmpy][tmpx - 1] == 1 && visit[tmpy][tmpx - 1] == 0){
                q.push({tmpy, tmpx - 1});
                visit[tmpy][tmpx - 1] = 1;
                result++;
            }
        }
        if (tmpy < mp.size() - 1){
            if (mp[tmpy + 1][tmpx] == 1 && visit[tmpy + 1][tmpx] == 0){
                q.push({tmpy + 1, tmpx});
                visit[tmpy + 1][tmpx] = 1;
                result++;
            }
        }
        if (tmpx < mp[0].size() - 1){
            if (mp[tmpy][tmpx + 1] == 1 && visit[tmpy][tmpx + 1] == 0){
                q.push({tmpy, tmpx + 1});
                visit[tmpy][tmpx + 1] = 1;
                result++;
            }
        }
    }
    return result * notEdge;
}

int main(){
    int n, m;
    cin >> n >> m;
    int result = 0;
    vector<vector<int>> mp(n, vector<int>(m, 0));
    vector<vector<int>> visit(n, vector<int>(m, 0));
    for (int i = 0; i < n; i++){
        for (int j = 0; j < m; j++){
            cin >> mp[i][j];
        }
    }
    for (int i = 0; i < mp.size(); i++){
        for (int j = 0; j < mp[0].size(); j++){
            if (mp[i][j] == 1 && visit[i][j] == 0){
                result += bfs(mp, visit, i, j);
            }
        }
    }
    cout << result;
    return 0;
}

bfs的版本，bfs不需要做递归回溯，所以函数的变量还是不变，只需要在内部增加一个标记是否有边缘元素的变量即可。

101. 孤岛的总面积