Toolbox: Dijkstra's

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Toolbox: Dijkstra's Shortest Path Algorithm

What is it?

Dijkstra's is a shortest path algorithm especially optimized for sparse graphs.

Code?

Optimized (+ priority queue - needs <queue>)

struct value
{
    int dat, val; constexpr bool operator<( const value& rhs) const { return val > rhs.val; }
};

priority_queue<value> pq;
vector<value> elist[805];

void dj(int st)
{
    memset(tmp, 63, sizeof tmp);
    tmp[st] = 0;
    pq.push({st, 0});
    while(!pq.empty())
    {
        value u = pq.top(); pq.pop();
        if(tmp[u.dat] != u.val) continue;
        for(value x:elist[u.dat]) // if C++11 incomaptible, change
        {
            int alt = u.val + x.val;
            if(alt < tmp[x.dat]) { tmp[x.dat] = alt; pq.push({x.dat, alt}); }
        }
    }
}

Explanation?

Dependencies

  • <vector>, <queue>
  • C++ 11 or above
  • st, starting point
  • Edge list in elist

Outputs

  • tmp, array of distances between starting point and any point

You're welcome.

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