给定四个数字， 生成四个数字能构成的所有表达式树

ab*c*d*
ab*c*d+
ab*c*d-
ab*c*d/
ab*c+d*
ab*c+d+
ab*c+d-
ab*c+d/
ab*c-d*
ab*c-d+
ab*c-d-
ab*c-d/
ab*c/d+
ab*c/d-
ab*c/d/
ab*cd*+
ab*cd*-
ab*cd+*
ab*cd+/
ab*cd-*
ab*cd-/
ab*cd/+
ab*cd/-
ab*d*c+
ab*d*c-
ab*d*c/
ab*d+c*
ab*d+c/
ab*d-c*
ab*d-c/
ab*d/c+
ab*d/c-
ab*dc-*
ab*dc-/
ab*dc/+
ab*dc/-
ab+c*d*
ab+c*d+
ab+c*d-
ab+c*d/
ab+c+d*
ab+c+d+
ab+c+d-
ab+c+d/
ab+c-d*
ab+c-d+
ab+c-d-
ab+c-d/
ab+c/d+
ab+c/d-
ab+c/d/
ab+cd*+
ab+cd*-
ab+cd+*
ab+cd+/
ab+cd-*
ab+cd-/
ab+cd/+
ab+cd/-
ab+d*c+
ab+d*c-
ab+d*c/
ab+d+c*
ab+d+c/
ab+d-c*
ab+d-c/
ab+d/c+
ab+d/c-
ab+dc-*
ab+dc-/
ab+dc/+
ab+dc/-
ab-c*d*
ab-c*d+
ab-c*d-
ab-c*d/
ab-c+d*
ab-c+d+
ab-c+d-
ab-c+d/
ab-c-d*
ab-c-d+
ab-c-d-
ab-c-d/
ab-c/d+
ab-c/d-
ab-c/d/
ab-cd*+
ab-cd*-
ab-cd+*
ab-cd+/
ab-cd-*
ab-cd-/
ab-cd/+
ab-cd/-
ab-d*c+
ab-d*c-
ab-d*c/
ab-d+c*
ab-d+c/
ab-d-c*
ab-d-c/
ab-d/c+
ab-d/c-
ab-dc/+
ab-dc/-
ab/c+d*
ab/c+d+
ab/c+d-
ab/c+d/
ab/c-d*
ab/c-d+
ab/c-d-
ab/c-d/
ab/c/d+
ab/c/d-
ab/c/d/
ab/cd*+
ab/cd*-
ab/cd+/
ab/cd-/
ab/cd/+
ab/cd/-
ab/d+c*
ab/d+c/
ab/d-c*
ab/d-c/
ab/d/c+
ab/d/c-
ab/dc-/
ab/dc/+
ab/dc/-
abc*+d*
abc*+d+
abc*+d-
abc*+d/
abc*-d*
abc*-d+
abc*-d-
abc*-d/
abc*d*+
abc*d*-
abc*d+*
abc*d+/
abc*d-*
abc*d-/
abc*d/+
abc*d/-
abc+*d*
abc+*d+
abc+*d-
abc+*d/
abc+/d+
abc+/d-
abc+/d/
abc+d*+
abc+d*-
abc+d+*
abc+d+/
abc+d-*
abc+d-/
abc+d/+
abc+d/-
abc-*d*
abc-*d+
abc-*d-
abc-*d/
abc-/d+
abc-/d-
abc-/d/
abc-d*+
abc-d*-
abc-d+*
abc-d+/
abc-d-*
abc-d-/
abc-d/+
abc-d/-
abc/+d*
abc/+d+
abc/+d-
abc/+d/
abc/-d*
abc/-d+
abc/-d-
abc/-d/
abc/d+*
abc/d+/
abc/d-*
abc/d-/
abc/d/+
abc/d/-
abcd*+*
abcd*+/
abcd*-*
abcd*-/
abcd+*+
abcd+*-
abcd+/+
abcd+/-
abcd-*+
abcd-*-
abcd-/+
abcd-/-
abcd/+*
abcd/+/
abcd/-*
abcd/-/
abd*+c*
abd*+c+
abd*+c-
abd*+c/
abd*-c*
abd*-c+
abd*-c-
abd*-c/
abd*c+*
abd*c+/
abd*c-*
abd*c-/
abd*c/+
abd*c/-
abd+*c*
abd+*c+
abd+*c-
abd+*c/
abd+/c+
abd+/c-
abd+/c/
abd+c*+
abd+c*-
abd+c/+
abd+c/-
abd-*c*
abd-*c+
abd-*c-
abd-*c/
abd-/c+
abd-/c-
abd-/c/
abd-c*+
abd-c*-
abd-c/+
abd-c/-
abd/+c*
abd/+c+
abd/+c-
abd/+c/
abd/-c*
abd/-c+
abd/-c-
abd/-c/
abd/c+*
abd/c+/
abd/c-*
abd/c-/
abdc/+*
abdc/+/
abdc/-*
abdc/-/
ac*b+d*
ac*b+d+
ac*b+d-
ac*b+d/
ac*b-d*
ac*b-d+
ac*b-d-
ac*b-d/
ac*b/d+
ac*b/d-
ac*b/d/
ac*bd*+
ac*bd*-
ac*bd+/
ac*bd-/
ac*bd/+
ac*bd/-
ac*d*b+
ac*d*b-
ac*d*b/
ac*d+b*
ac*d+b/
ac*d-b*
ac*d-b/
ac*d/b+
ac*d/b-
ac*db-/
ac*db/+
ac*db/-
ac+b*d*
ac+b*d+
ac+b*d-
ac+b*d/
ac+b/d+
ac+b/d-
ac+b/d/
ac+bd+*
ac+bd+/
ac+bd-*
ac+bd-/
ac+d*b+
ac+d*b-
ac+d*b/
ac+d+b*
ac+d+b/
ac+d-b*
ac+d-b/
ac+d/b+
ac+d/b-
ac+db-*
ac+db-/
ac+db/+
ac+db/-
ac-b*d*
ac-b*d+
ac-b*d-
ac-b*d/
ac-b/d+
ac-b/d-
ac-b/d/
ac-bd+*
ac-bd+/
ac-bd-*
ac-bd-/
ac-d*b+
ac-d*b-
ac-d*b/
ac-d+b*
ac-d+b/
ac-d-b*
ac-d-b/
ac-d/b+
ac-d/b-
ac-db/+
ac-db/-
ac/b+d*
ac/b+d+
ac/b+d-
ac/b+d/
ac/b-d*
ac/b-d+
ac/b-d-
ac/b-d/
ac/bd*+
ac/bd*-
ac/bd/+
ac/bd/-
ac/d+b*
ac/d+b/
ac/d-b*
ac/d-b/
ac/d/b+
ac/d/b-
ac/db/+
ac/db/-
acb-*d*
acb-*d-
acb-*d/
acb-/d-
acb-/d/
acb-d-*
acb-d-/
acb/+d*
acb/+d+
acb/+d-
acb/+d/
acb/-d*
acb/-d+
acb/-d-
acb/-d/
acb/d+*
acb/d+/
acb/d-*
acb/d-/
acb/d/+
acb/d/-
acbd*-*
acbd*-/
acbd+/+
acbd+/-
acbd-/+
acbd-/-
acbd/-*
acbd/-/
acd*+b*
acd*+b/
acd*-b*
acd*-b/
acd*b-*
acd*b-/
acd*b/+
acd*b/-
acd+*b+
acd+*b-
acd+*b/
acd+/b+
acd+/b-
acd+b-*
acd+b-/
acd+b/+
acd+b/-
acd-*b+
acd-*b-
acd-*b/
acd-/b+
acd-/b-
acd-b/+
acd-b/-
acd/+b*
acd/+b/
acd/-b*
acd/-b/
acd/b-*
acd/b-/
acdb/+*
acdb/+/
acdb/-*
acdb/-/
ad*b+c*
ad*b+c+
ad*b+c-
ad*b+c/
ad*b-c*
ad*b-c+
ad*b-c-
ad*b-c/
ad*b/c+
ad*b/c-
ad*b/c/
ad*bc*+
ad*bc*-
ad*bc+/
ad*bc-/
ad*bc/+
ad*bc/-
ad*c+b*
ad*c+b/
ad*c-b*
ad*c-b/
ad*c/b+
ad*c/b-
ad*cb-/
ad*cb/+
ad*cb/-
ad+b*c*
ad+b*c+
ad+b*c-
ad+b*c/
ad+b/c+
ad+b/c-
ad+b/c/
ad+bc+*
ad+bc+/
ad+bc-*
ad+bc-/
ad+c*b+
ad+c*b-
ad+c*b/
ad+c/b+
ad+c/b-
ad+cb-*
ad+cb-/
ad-b*c*
ad-b*c+
ad-b*c-
ad-b*c/
ad-b/c+
ad-b/c-
ad-b/c/
ad-bc+*
ad-bc+/
ad-bc-*
ad-bc-/
ad-c*b+
ad-c*b-
ad-c*b/
ad-c/b+
ad-c/b-
ad/b+c*
ad/b+c+
ad/b+c-
ad/b+c/
ad/b-c*
ad/b-c+
ad/b-c-
ad/b-c/
ad/bc*+
ad/bc*-
ad/bc/+
ad/bc/-
ad/c+b*
ad/c+b/
ad/c-b*
ad/c-b/
ad/cb/+
ad/cb/-
adb-*c*
adb-*c-
adb-*c/
adb-/c-
adb-/c/
adb-c-*
adb-c-/
adb/+c*
adb/+c/
adb/-c*
adb/-c/
adb/c-*
adb/c-/
adb/c/+
adb/c/-
adbc*-*
adbc*-/
adbc+/+
adbc+/-
adbc-/+
adbc-/-
adbc/-*
adbc/-/
adc-*b-
adc-*b/
adc-/b-
adc/+b*
adc/+b/
adc/-b*
adc/-b/
adc/b-*
adc/b-/
adcb/-*
adcb/-/
ba-c*d*
ba-c*d-
ba-c*d/
ba-c-d*
ba-c-d-
ba-c-d/
ba-c/d-
ba-c/d/
ba-cd*-
ba-cd+*
ba-cd+/
ba-cd-*
ba-cd-/
ba-cd/-
ba-d*c-
ba-d*c/
ba-d-c*
ba-d-c/
ba-d/c-
ba-dc/-
ba/c+d*
ba/c+d+
ba/c+d-
ba/c+d/
ba/c-d*
ba/c-d+
ba/c-d-
ba/c-d/
ba/c/d+
ba/c/d-
ba/c/d/
ba/cd*+
ba/cd*-
ba/cd+/
ba/cd-/
ba/cd/+
ba/cd/-
ba/d+c*
ba/d+c/
ba/d-c*
ba/d-c/
ba/d/c+
ba/d/c-
ba/dc-/
ba/dc/+
ba/dc/-
bac*-d*
bac*-d-
bac*-d/
bac*d*-
bac*d+/
bac*d-/
bac*d/-
bac+/d+
bac+/d-
bac+/d/
bac+d*-
bac+d+/
bac+d-/
bac+d/-
bac-/d+
bac-/d-
bac-/d/
bac-d*-
bac-d+/
bac-d-/
bac-d/-
bac/-d*
bac/-d-
bac/-d/
bac/d+/
bac/d-/
bac/d/-
bacd*+/
bacd*-/
bacd+*-
bacd+/-
bacd-*-
bacd-/-
bacd/+/
bacd/-/
bad*-c*
bad*-c-
bad*-c/
bad*c+/
bad*c-/
bad*c/-
bad+/c+
bad+/c-
bad+/c/
bad+c*-
bad+c/-
bad-/c+
bad-/c-
bad-/c/
bad-c*-
bad-c/-
bad/-c*
bad/-c-
bad/-c/
bad/c+/
bad/c-/
badc/+/
badc/-/
bc*a-d*
bc*a-d-
bc*a-d/
bc*a/d+
bc*a/d-
bc*a/d/
bc*ad*-
bc*ad+/
bc*ad-/
bc*ad/-
bc*d*a-
bc*d*a/
bc*d+a-
bc*d+a/
bc*d-a/
bc*d/a-
bc*da-/
bc*da/+
bc*da/-
bc+a-d*
bc+a-d-
bc+a-d/
bc+a/d+
bc+a/d-
bc+a/d/
bc+ad*-
bc+ad+/
bc+ad-/
bc+ad/-
bc+d*a-
bc+d*a/
bc+d+a-
bc+d+a/
bc+d-a/
bc+d/a-
bc+da-/
bc+da/+
bc+da/-
bc-a/d+
bc-a/d-
bc-a/d/
bc-ad+/
bc-ad-/
bc-d*a-
bc-d*a/
bc-d+a/
bc-d-a/
bc-d/a-
bc-da/+
bc-da/-
bc/a-d*
bc/a-d-
bc/a-d/
bc/ad*-
bc/ad/-
bc/d+a-
bc/d+a/
bc/d-a/
bc/d/a-
bc/da/+
bc/da/-
bca-/d-
bca-/d/
bca-d-/
bca/+d*
bca/+d+
bca/+d-
bca/+d/
bca/-d*
bca/-d+
bca/-d-
bca/-d/
bca/d+*
bca/d+/
bca/d-*
bca/d-/
bca/d/+
bca/d/-
bcad*-/
bcad+/+
bcad+/-
bcad-/+
bcad-/-
bcad/-/
bcd*+a-
bcd*+a/
bcd*-a/
bcd*a-/
bcd*a/+
bcd*a/-
bcd+*a-
bcd+*a/
bcd+/a-
bcd+a-/
bcd+a/+
bcd+a/-
bcd-*a-
bcd-*a/
bcd-/a-
bcd-a/+
bcd-a/-
bcd/+a-
bcd/+a/
bcd/-a/
bcd/a-/
bcda/+*
bcda/+/
bcda/-*
bcda/-/
bd*a-c*
bd*a-c-
bd*a-c/
bd*a/c+
bd*a/c-
bd*a/c/
bd*ac*-
bd*ac+/
bd*ac-/
bd*ac/-
bd*c+a-
bd*c+a/
bd*c-a/
bd*c/a-
bd*ca-/
bd*ca/+
bd*ca/-
bd+a-c*
bd+a-c-
bd+a-c/
bd+a/c+
bd+a/c-
bd+a/c/
bd+ac*-
bd+ac+/
bd+ac-/
bd+ac/-
bd+c*a-
bd+c*a/
bd+c/a-
bd+ca-/
bd-a/c+
bd-a/c-
bd-a/c/
bd-ac+/
bd-ac-/
bd-c*a-
bd-c*a/
bd-c/a-
bd/a-c*
bd/a-c-
bd/a-c/
bd/ac*-
bd/ac/-
bd/c+a-
bd/c+a/
bd/c-a/
bd/ca/+
bd/ca/-
bda-/c-
bda-/c/
bda-c-/
bda/+c*
bda/+c/
bda/-c*
bda/-c/
bda/c-*
bda/c-/
bda/c/+
bda/c/-
bdac*-/
bdac+/+
bdac+/-
bdac-/+
bdac-/-
bdac/-/
bdc-*a-
bdc-*a/
bdc-/a-
bdc/+a-
bdc/+a/
bdc/-a/
bdc/a-/
bdca/-*
bdca/-/
ca-b*d*
ca-b*d-
ca-b*d/
ca-b-d*
ca-b-d-
ca-b-d/
ca-b/d-
ca-b/d/
ca-bd*-
ca-bd+*
ca-bd+/
ca-bd-*
ca-bd-/
ca-bd/-
ca-d*b-
ca-d*b/
ca-d-b*
ca-d-b/
ca-d/b-
ca-db/-
ca/b-d*
ca/b-d-
ca/b-d/
ca/b/d+
ca/b/d-
ca/b/d/
ca/bd*-
ca/bd+/
ca/bd-/
ca/bd/-
ca/d+b-
ca/d+b/
ca/d-b/
ca/d/b-
ca/db-/
ca/db/+
ca/db/-
cab*-d*
cab*-d-
cab*-d/
cab*d*-
cab*d+/
cab*d-/
cab*d/-
cab+/d+
cab+/d-
cab+/d/
cab+d*-
cab+d+/
cab+d-/
cab+d/-
cab-/d+
cab-/d-
cab-/d/
cab-d*-
cab-d+/
cab-d-/
cab-d/-
cab/-d*
cab/-d-
cab/-d/
cab/d+/
cab/d-/
cab/d/-
cabd*+/
cabd*-/
cabd+*-
cabd+/-
cabd-*-
cabd-/-
cabd/+/
cabd/-/
cad*-b*
cad*-b-
cad*-b/
cad*b+/
cad*b-/
cad*b/-
cad+/b-
cad+/b/
cad+b*-
cad+b/-
cad-/b-
cad-/b/
cad-b*-
cad-b/-
cad/-b*
cad/-b-
cad/-b/
cad/b+/
cad/b-/
cadb/+/
cadb/-/
cb-a/d-
cb-a/d/
cb-ad+/
cb-ad-/
cb-d*a-
cb-d*a/
cb-d-a/
cb-d/a-
cb-da/-
cb/a-d*
cb/a-d-
cb/a-d/
cb/ad*-
cb/ad/-
cb/d+a-
cb/d+a/
cb/d-a/
cb/d/a-
cb/da/+
cb/da/-
cba-/d-
cba-/d/
cba-d-/
cba/-d*
cba/-d-
cba/-d/
cba/d+/
cba/d-/
cba/d/-
cbad*-/
cbad+/-
cbad-/-
cbad/-/
cbd*-a/
cbd*a-/
cbd*a/-
cbd+/a-
cbd+a-/
cbd+a/-
cbd-/a-
cbd-a/-
cbd/-a/
cbd/a-/
cbda/+/
cbda/-/
cd*a-b*
cd*a-b-
cd*a-b/
cd*a/b-
cd*a/b/
cd*ab*-
cd*ab+/
cd*ab-/
cd*ab/-
cd*b-a/
cd*b/a-
cd*ba-/
cd*ba/-
cd+a-b*
cd+a-b-
cd+a-b/
cd+a/b-
cd+a/b/
cd+ab*-
cd+ab+/
cd+ab-/
cd+ab/-
cd+b-a/
cd+b/a-
cd+ba-/
cd+ba/-
cd-a/b-
cd-a/b/
cd-ab+/
cd-ab-/
cd-b/a-
cd/a-b*
cd/a-b-
cd/a-b/
cd/ab*-
cd/ab/-
cd/b-a/
cd/ba/-
cda-/b-
cda-/b/
cda-b-/
cda/+b-
cda/+b/
cda/-b/
cda/b-/
cda/b/+
cda/b/-
cdab*-/
cdab+/+
cdab+/-
cdab-/+
cdab-/-
cdab/-/
cdb-/a-
cdb/+a-
cdb/+a/
cdb/-a/
cdb/a-/
cdba/-/
da-b*c*
da-b*c-
da-b*c/
da-b-c*
da-b-c-
da-b-c/
da-b/c-
da-b/c/
da-bc*-
da-bc+*
da-bc+/
da-bc-*
da-bc-/
da-bc/-
da-c*b-
da-c*b/
da-c-b*
da-c-b/
da-c/b-
da-cb/-
da/b-c*
da/b-c-
da/b-c/
da/b/c-
da/b/c/
da/bc*-
da/bc+/
da/bc-/
da/bc/-
da/c-b/
da/c/b-
da/cb-/
da/cb/-
dab*-c*
dab*-c-
dab*-c/
dab*c*-
dab*c+/
dab*c-/
dab*c/-
dab+/c-
dab+/c/
dab+c*-
dab+c+/
dab+c-/
dab+c/-
dab-/c-
dab-/c/
dab-c*-
dab-c+/
dab-c-/
dab-c/-
dab/-c*
dab/-c-
dab/-c/
dab/c+/
dab/c-/
dab/c/-
dabc*+/
dabc*-/
dabc+*-
dabc+/-
dabc-*-
dabc-/-
dabc/+/
dabc/-/
dac*-b*
dac*-b-
dac*-b/
dac*b+/
dac*b-/
dac*b/-
dac+/b-
dac+/b/
dac+b*-
dac+b/-
dac-/b-
dac-/b/
dac-b*-
dac-b/-
dac/-b*
dac/-b-
dac/-b/
dac/b+/
dac/b-/
dacb/+/
dacb/-/
db-a/c-
db-a/c/
db-ac+/
db-ac-/
db-c*a-
db-c*a/
db-c-a/
db-c/a-
db-ca/-
db/a-c*
db/a-c-
db/a-c/
db/ac*-
db/ac/-
db/c-a/
db/c/a-
db/ca/-
dba-/c-
dba-/c/
dba-c-/
dba/-c*
dba/-c-
dba/-c/
dba/c+/
dba/c-/
dba/c/-
dbac*-/
dbac+/-
dbac-/-
dbac/-/
dbc*-a/
dbc*a-/
dbc*a/-
dbc+/a-
dbc+a-/
dbc+a/-
dbc-/a-
dbc-a/-
dbc/-a/
dbc/a-/
dbca/+/
dbca/-/
dc-a/b-
dc-a/b/
dc-ab+/
dc-ab-/
dc-b/a-
dc/a-b*
dc/a-b-
dc/a-b/
dc/ab*-
dc/ab/-
dc/b-a/
dc/ba/-
dca-/b-
dca-/b/
dca-b-/
dca/-b/
dca/b-/
dca/b/-
dcab*-/
dcab+/-
dcab-/-
dcab/-/
dcb-/a-
dcb/-a/
dcb/a-/
dcba/-/