Problem CSTREET from SPOJ

CSTREET.cpp

@@ -0,0 +1,154 @@
+// Problem : CSTREET from SPOJ
+
+#include <bits/stdc++.h>
+using namespace std;
+#define INF 1000000000
+
+class Heap{
+	// pos, ele are inverse of each other
+	int *ele,*pos,*key;
+	int size;
+
+	void swap(int idx1, int idx2){
+		ele[idx1] = ele[idx1] + ele[idx2] - (ele[idx2] = ele[idx1]);
+		pos[ele[idx1]] = idx1;
+		pos[ele[idx2]] = idx2;
+	}
+
+	void siftUp(int idx){
+		while(idx>0 && key[ele[idx]]<key[ele[(idx-1)/2]]){
+			swap(idx,(idx-1)/2);
+			idx = (idx-1)/2;
+		}
+	}
+
+	void siftDown(int idx){
+		int v1,v2;
+		while(idx < size){
+			v1 = ((2*idx+1 < size)?key[ele[2*idx+1]]:INF);
+			v2 = ((2*idx+2 < size)?key[ele[2*idx+2]]:INF);
+
+			if(min(v1,v2) < key[ele[idx]]){
+				if(v1 < v2){
+					swap(idx,2*idx+1);
+					idx = 2*idx+1;
+				}
+				else{
+					swap(idx,2*idx+2);
+					idx = 2*idx+2;
+				}
+			}
+			else{
+				break;
+			}
+		}
+	}
+
+public:
+	Heap(int N){
+		ele = new int[N];
+		pos = new int[N];
+		key = new int[N];
+		size = 0;
+
+		int i;
+		for(i=0;i<N;i++)ele[i] = pos[i] = key[i] = INF;
+
+	}
+
+	int insert(int city,int key){
+		pos[city] = size;
+		ele[size] = city;
+		this->key[city] = key;
+		size++;
+		siftUp(size-1);
+	}
+
+	int deleteMin(){
+		int city = ele[0];
+		pos[city] = key[city] = INF;
+		ele[0] = ele[size-1];
+		pos[ele[0]] = 0;
+		size--;
+		siftDown(0);
+		return city;
+	}
+
+	void decreaseKey(int city, int val){
+		key[city] = val;
+		siftUp(pos[city]);
+	}	
+
+	bool empty(){
+		return size==0;
+	}
+
+	bool contains(int city){
+		return pos[city]!=INF;
+	}
+
+	void printHeap(){
+		int i;
+		cout<<"Heap: ";
+		for(i=0;i<size;i++){
+			cout<<"("<<ele[i]<<","<<key[ele[i]]<<") - ";
+		}
+		cout<<"\n";
+	}
+
+};
+
+
+void solve(){
+	int n,m,i,j,a,b,wt,cur;
+	long long p;
+	cin>>p>>n>>m;
+
+	vector<int> adj[n];
+	vector<int> wei[n];
+	int dist[n];
+	bool visit[n];
+
+	while(m--){
+		cin>>a>>b>>wt;
+		adj[a-1].push_back(b-1);
+		adj[b-1].push_back(a-1);
+		wei[a-1].push_back(wt);
+		wei[b-1].push_back(wt);
+	}
+
+	for(i=0;i<n;i++)dist[i] = INF,visit[i] = false;
+
+	long long res = 0;
+	Heap heap(n);
+	heap.insert(0,0);
+	dist[0] = 0;
+
+	while(!heap.empty()){
+		cur = heap.deleteMin();
+		visit[cur] = true;
+		res+=dist[cur];
+		for(i=0;i<adj[cur].size();i++){
+			if(!visit[adj[cur][i]] && wei[cur][i] < dist[adj[cur][i]]){
+				dist[adj[cur][i]] = wei[cur][i];
+				if(heap.contains(adj[cur][i])){
+					heap.decreaseKey(adj[cur][i],dist[adj[cur][i]]);
+				}
+				else{
+					heap.insert(adj[cur][i],dist[adj[cur][i]]);
+				}
+			}
+		}
+	}
+
+	cout<<res*p<<"\n";
+	return ;
+}
+
+
+int main(){
+	int t;
+	cin>>t;
+	while(t--)solve();
+	return 0;
+}