algorithms_and_structures/417_Pacific_Atlantic_water_flow.txt at main · Alegu3rra/algorithms_and_structures · GitHub

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class Solution {
public:
    int coord[4][2] = {{-1,0}, {0,-1}, {0,1},{1,0}};
    bool visited[200][200];
    bool isPossible(int i,int  j, int n,int  m){
        return i < n && i >= 0 && j < m && j >= 0 && visited[i][j] != true;
    }
    set<pair<int, int>> dfs(vector<vector<int>>& heights, queue<pair<int, int>>& currentQueue, set<pair<int, int>>& resOcean){

        int n = heights.size();
        int m = heights[0].size();

        while(!currentQueue.empty()){
            pair<int, int> currHeight = currentQueue.front();
            currentQueue.pop();
            int x = currHeight.first;
            int y = currHeight.second;

            for(int k = 0; k < 4; k++){
                int nextx = x + coord[k][0];
                int nexty = y + coord[k][1];

                if(isPossible( nextx, nexty, n, m)){
                    if(heights[x][y] <= heights[nextx][nexty]){
                        currentQueue.push({nextx, nexty});
                        visited[nextx][nexty] = true;
                        resOcean.insert({nextx, nexty});
                    }
                }
            }
        }
        return resOcean;
    }

    vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {

        queue<pair<int, int>> queueP;
        queue<pair<int, int>> queueA;
        set<pair<int, int>> coorP;
        set<pair<int, int>> coorA;

        int n = heights.size();
        int m = heights[0].size();

        memset(visited, false, sizeof(visited));
        // pacific fill
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(i == 0 || j == 0){
                    queueP.push({i,j});
                    visited[i][j] = true;
                    coorP.insert({i,j});
                }
            }
        }
        set<pair<int, int>> resP = dfs(heights, queueP, coorP);

        memset(visited, false, sizeof(visited));
        // Atlantic fill
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(i == n-1 || j == m-1){
                    queueA.push({i,j});
                    visited[i][j] = true;
                    coorA.insert({i,j});
                }
            }
        }
        set<pair<int, int>> resA = dfs(heights, queueA, coorA);


        set<pair<int,int>> interseccion;

        set_intersection(resP.begin(), resP.end(),
                     resA.begin(), resA.end(),
                     inserter(interseccion, interseccion.begin()));

        vector<vector<int>> island;
        for( auto item : interseccion){
            island.push_back({item.first, item.second});
        }
        return island;
    }

};