Spfa algorithm Template

Const maxp = 10000; {maximum number of knots} var P, C, S, T: longint; {P, number of knots; C, number of edges; s: start point; t: destination} A, B: array [1 .. maxp, 0 .. maxp] of longint; {A [x, y] stores the right of the edge between x and y; B [x, c] store another node of the Side C connected to x, y} D: array [1 .. maxp] of integer; {queue} V: array [1 .. maxp] of Boolean; {indicates whether to join the queue} Dist: array [1 .. maxp] of longint; {the shortest path from the start} head, tail: longint; {head/tail pointer} procedure Init; var I, x, y, z: longint; begin read (p, c); for I: = 1 to C do begin readln (x, y, z); {X, Y: two nodes of an edge; Z: the weight of this edge} Inc (B [x, 0]); B [X, B [x, 0]: = y; A [x, y]: = z; {B [x, 0]: Number of edges with X as a node} Inc (B [y, 0]); B [y, B [y, B [y, 0]: = x; A [y, X]: = z; end; readln (S, T); {read start and end} end; Procedure spfa (s: longint); {spfa} var I, j, now, sum: longint; begin fillchar (D, sizeof (D), 0); fillchar (v, sizeof (V ), false); For J: = 1 to P do Dist [J]: = maxlongint; Dist [s]: = 0; V [s]: = true; d [1]: = s; {initial status of the queue, s as the starting point} head: = 1; tail: = 1; while head <= tail do {the queue is not empty} begin now: = d [head]; {first element} For I: = 1 to B [now, 0] Do if Dist [B [now, i]> Dist [now] + A [now, B [now, I] Then begin Dist [B [now, I]: = DIST [now] + A [now, B [now, I]; {change the Shortest Path} if not V [B [now, i] Then {extended node into the queue} begin Inc (tail); D [tail]: = B [now, I]; V [B [now, I]: = true; end; V [now]: = false; {release node} Inc (head); {team} end; Procedure print; begin writeln (Dist [T]); end; begin Init; spfa (s); print; end.