Create NumberOfIslands-II.cpp

Graphs/NumberOfIslands-II.cpp

@@ -0,0 +1,96 @@
+// User function Template for C++
+class DisjointSet {
+    public:
+        vector<int> rank, parent;
+
+        DisjointSet(int n) {
+            rank.resize(n+1, 0);
+            parent.resize(n+1);
+
+            for(int i=0; i<=n; i++) {
+                parent[i] = i;
+            }
+        }
+
+        int findUParent(int node) {
+            if(parent[node] == node)
+                return node;
+
+            return parent[node] = findUParent(parent[node]);
+        }
+
+        void unionByRank(int u, int v) {
+            int ul_parent_u = findUParent(u);
+            int ul_parent_v = findUParent(v);
+
+            if(ul_parent_u == ul_parent_v)
+                return;
+
+            if(rank[ul_parent_u] < rank[ul_parent_v]) {
+                parent[ul_parent_u] = ul_parent_v;
+            }
+            else if(rank[ul_parent_v] < rank[ul_parent_u]) {
+                parent[ul_parent_v] = ul_parent_u;
+            }
+            else {
+                parent[ul_parent_v] = ul_parent_u;
+                rank[ul_parent_u]++;
+            }
+        }
+};
+
+class Solution {
+    private:
+    bool isValid(int nrow,int ncol,int n,int m){
+        return nrow>=0 && nrow<n && ncol>=0 && ncol<m;
+    }
+  public:
+    vector<int> numOfIslands(int n, int m, vector<vector<int>> &operators) {
+        // code here
+        DisjointSet ds(n*m);
+        int vis[n][m];
+        memset(vis,0,sizeof vis);
+        int cnt=0;
+        vector<int>ans;
+
+        for(auto it:operators){
+            int row=it[0];
+            int col=it[1];
+            if(vis[row][col]==1){
+                ans.push_back(cnt);
+                continue;
+            }
+
+            vis[row][col]=1;
+            cnt++;
+            // row-1,col
+            // row,col+1
+            // row+1,col
+            // row,col-1
+            int dr[]={-1,0,+1,0};
+            int dc[]={0,1,0,-1};
+
+            for(int ind=0;ind<4;ind++){
+                int nrow=row+dr[ind];
+                int ncol=col+dc[ind];
+                if(isValid(nrow,ncol,n,m)){
+                    if(vis[nrow][ncol]==1){
+                        int nodeNo=row*m+col;
+                        int adjNodeNo=nrow*m+ncol;
+                        if(ds.findUParent(nodeNo)!=ds.findUParent(adjNodeNo)){
+                            cnt--;
+                            ds.unionByRank(nodeNo,adjNodeNo);
+                        }
+                    }
+                }
+
+            }
+            ans.push_back(cnt);
+        }
+
+
+
+        return ans;
+
+    }
+};