function BACKTRACKING-SEARCH(csp) returns a solution, or failure
return RECURSIVE- BACKTRACKING({ }, csp)
function RECURSIVE-BACKTRACKING(assignment,csp) returns a solution, or failure
if assignment is complete then
return assignment
var ←SELECT-UNASSIGNED-VARIABLE(VARIABLES[csp],assignment,csp)
for each value in ORDER-DOMAIN-VALUES(var,assignment,csp) do
if value is consistent with assignment according to CONSTRAINTS[csp] then
add {var = value} to assignment
result ← RECURSIVE-BACKTRACKING(assignment, csp)
if result ̸= failure then
return result
remove {var = value} from assignment
return failure
這是來自AIMA的回溯遞歸算法僞代碼。但是,我不明白它是否會返回所有可能的解決方案或只是找到第一個解決方案。如果是最後一個選項,請幫我修改它以返回可能的解決方案列表(或者至少更新一些全局列表)。用多種解決方案遞歸回溯
編輯:我用Java實現了這個算法。但是,有一個問題:
如果我沒有返回賦值,但將其保存在結果而不是遞歸停止條件失敗(即它不再存在)。我怎樣才能實現另一種停止條件?也許我應該回到真的到底?
這裏是我的代碼:
/**
* The actual backtracking. Unfortunately, I don't have time to implement LCV or MCV,
* therefore it will be just ordinary variable-by-variable search.
* @param line
* @param onePossibleSituation
* @param result
*/
public static boolean recursiveBacktrack(Line line, ArrayList<Integer> onePossibleSituation, ArrayList<ArrayList<Integer>> result){
if (onePossibleSituation.size() == line.getNumOfVars()){
// instead of return(assignment)
ArrayList<Integer> situationCopy = new ArrayList<Integer>();
situationCopy.addAll(onePossibleSituation);
result.add(situationCopy);
onePossibleSituation.clear();
}
Block variableToAssign = null;
// iterate through all variables and choose one unassigned
for(int i = 0; i < line.getNumOfVars(); i++){
if(!line.getCspMiniTaskVariables().get(i).isAssigned()){
variableToAssign = line.getCspMiniTaskVariables().get(i);
break;
}
}
// for each domain value for given block
for (int i = line.getCspMiniTaskDomains().get(variableToAssign.getID())[0];
i <= line.getCspMiniTaskDomains().get(variableToAssign.getID())[0]; i++){
if(!areThereConflicts(line, onePossibleSituation)){
//complete the assignment
variableToAssign.setStartPositionTemporary(i);
variableToAssign.setAssigned(true);
onePossibleSituation.add(i);
//do backtracking
boolean isPossibleToPlaceIt = recursiveBacktrack(line,onePossibleSituation,result);
if(!isPossibleToPlaceIt){
return(false);
}
}
// unassign
variableToAssign.setStartPositionTemporary(-1);
variableToAssign.setAssigned(false);
onePossibleSituation.remove(i);
}
// end of backtracking
return(false);
}
更新了我關於您的實施的答案。 – dreamzor 2013-03-26 07:22:32