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Depth First Search in ALGOL 60
Published on 17 April 2026 (Updated: 17 April 2026)
Welcome to the Depth First Search in ALGOL 60 page! Here, you'll find the source code for this program as well as a description of how the program works.
Current Solution
begin
procedure usage;
begin
outstring(
1,
"Usage: please provide a tree in an adjacency matrix form "
"(\"0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0\") "
"together with a list of vertex values (\"1, 3, 5, 2, 4\") "
"and the integer to find (\"4\")"
);
stop
end usage;
comment Input a digit character from stdin and return the following:
- "0" to "9" maps to 0 to 9
- "+" maps to 10
- "-" maps to 11
- whitespace maps to 12
- comma maps to 13
- null byte maps to -1
- invalid bytes map to -2;
integer procedure indigit;
begin
comment Mapping:
- "0" to "9" maps to 1 to 10
- "+" maps to 11
- "-" maps to 12
- "\t" maps to 13
- "\r" maps to 14
- "\n" maps to 15
- " " maps to 16
- "," maps to 17
- null byte maps to 18
- invalid byte maps to 0;
integer ch;
inchar(0, "0123456789+-\t\r\n ,", ch);
if ch < 1 then ch := -2
else if ch < 13 then ch := ch - 1
else if ch < 17 then ch := 12
else if ch = 17 then ch := 13
else ch := -1;
indigit := ch
end indigit;
comment Input an integer from stdin into 'result' and parse it.
The last character is read into 'ch'.
return true if integer is valid, false otherwise;
boolean procedure inValidInteger(result, ch, allowComma);
value allowComma;
integer result, ch;
boolean allowComma;
begin
boolean valid, commaFound;
integer s;
result := 0;
valid := false;
commaFound := false;
s := 1;
comment Ignore whitespace;
whiteloop:
ch := indigit;
if ch = 12 then goto whiteloop;
comment Process signs: ignore "+" and invert sign if "-";
signloop:
if ch = 10 | ch = 11 then
begin
if ch = 11 then s := -s;
ch := indigit;
goto signloop
end;
comment Indicate valid if "0" to "9";
if ch >= 0 & ch <= 9 then valid := true;
comment Process digits: update value;
valueloop:
if ch >= 0 & ch <= 9 then
begin
comment Invalid if overflow or underflow;
if (s > 0 & (maxint - ch) % 10 < result) |
(s < 0 & (-1 - maxint + ch) % 10 > result) then valid := false;
result := result * 10 + s * ch;
ch := indigit;
goto valueloop
end;
comment If comma not allowed, ignore characters until end
input. If comma allowed, ignore characters until comma
or end of input. Indicate if comma found;
ignoreloop:
if !(ch = -1 | (allowComma & ch = 13)) then
begin
if ch != 12 & ch != 13 then valid := false;
if ch = 13 then
begin
commaFound := true;
if !allowComma then valid := false
end;
ch := indigit;
goto ignoreloop
end;
comment If comma found, indicate last character is comma;
if commaFound then ch := 13;
inValidInteger := valid
end inValidInteger;
comment Returns length of array if valid, -1 otherwise;
integer procedure inIntegerArray(arr, maxLen);
value maxLen;
integer array arr;
integer maxLen;
begin
integer arrLen, val, ch;
boolean valid;
arrLen := 0;
comment Get value with possible comma (13). Indicate invalid,
if invalid integer. Otherwise, append value to array if
no invalid values and there is room;
itemloop:
if !inValidInteger(val, ch, true) then arrLen := -1
else if arrLen >= 0 & arrLen < maxLen then
begin
arrLen := arrLen + 1;
arr[arrLen] := val
end;
comment Repeat until end of input;
if ch != -1 then goto itemloop;
inIntegerArray := arrLen
end inIntegerArray;
comment Create graph from connection matrix and vertex values.
The graph is in this form:
- column 1: Vertex values
- column 2: Number of children for each vertex value
- column 3 ... n + 2: Index of each child
where n = number of vertices;
procedure createGraph(connMtx, connMtxLen, vert, vertLen, graph);
value connMtxLen, vertLen;
integer array connMtx, vert, graph;
integer connMtxLen, vertLen;
begin
integer i, j, idx;
idx := 0;
for i := 1 step 1 until vertLen do
begin
comment Store this vertex value and initialize number of children;
graph[i, 1] := vert[i];
graph[i, 2] := 0;
comment Connect child nodes for this vertex;
for j := 1 step 1 until vertLen do
begin
idx := idx + 1;
if idx <= connMtxLen then
begin
if connMtx[idx] != 0 then
begin
graph[i, 2] := graph[i, 2] + 1;
graph[i, graph[i, 2] + 2] := j
end
end
end
end
end createGraph;
comment Returns index if target value found, 0 otherwise;
integer procedure depthFirstSearch(graph, vertLen, target);
value vertLen, target;
integer array graph;
integer vertLen, target;
begin
integer procedure depthFirstSearchRec(visited, nodeIdx);
value nodeIdx;
boolean array visited;
integer nodeIdx;
begin
integer foundIdx, childIdx, i;
comment Indicate target value not found;
foundIdx := 0;
comment If node index is valid and value matches target, return
this node index;
if nodeIdx > 0 then
begin
if graph[nodeIdx, 1] = target then foundIdx := nodeIdx
else
begin
comment Otherwise, indicate node is visited;
visited[nodeIdx] := true;
comment Perform Depth First Search on each unvisited child of
this node (if any). Stop when target value is found;
i := 0;
searchloop:
i := i + 1;
if i <= graph[nodeIdx, 2] & foundIdx = 0 then
begin
childIdx := graph[nodeIdx, i + 2];
if !visited[childIdx] then
begin
foundIdx := depthFirstSearchRec(visited, childIdx);
visited[childIdx] := true
end;
goto searchloop
end
end
end;
depthFirstSearchRec := foundIdx
end depthFirstSearchRec;
integer i;
boolean array visited[1:vertLen];
comment Indicate no nodes visited;
for i := 1 step 1 until vertLen do visited[i] := false;
comment Do Depth First Search for target value starting at
root node (1);
depthFirstSearch := depthFirstSearchRec(visited, 1)
end depthFirstSearch;
integer argc, connMtxLen, vertLen, ch, target, idx;
integer array connMtx[1:256], vert[1:16];
comment Get number of parameters. Exit if too few;
ininteger(0, argc);
if argc < 3 then usage;
comment Get connection matrix input from 1st argument. Exit if invalid;
connMtxLen := inIntegerArray(connMtx, 256);
if connMtxLen < 1 then usage;
comment Get vertex values from 2nd argument. Exit if invalid;
vertLen := inIntegerArray(vert, 16);
if vertLen < 1 then usage;
comment Get target value from 3nd argument. Exit if invalid;
if !inValidInteger(target, ch, false) then usage;
begin
comment Create a graph from the connect matrix and vertex values;
integer array graph[1:vertLen, 1:vertLen + 2];
createGraph(connMtx, connMtxLen, vert, vertLen, graph);
comment Depth First Search for target value. Indicate if found;
idx := depthFirstSearch(graph, vertLen, target);
if idx > 0 then outstring(1, "true\n")
else outstring(1, "false\n")
end
end
Depth First Search in ALGOL 60 was written by:
- rzuckerm
If you see anything you'd like to change or update, please consider contributing.
How to Implement the Solution
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How to Run the Solution
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