# DFS solution in Python with more explanation

• ``````def addOperators(self, num, target):
"""
:type num: str
:type target: int
:rtype: List[str]
"""

def dfs(num, start, left_total, last, target, single, result):
if start == len(num):
if left_total == target: # condition to get a solution
result.append(single)
for i in range(start, len(num)):
if i > start and int(num[start:i]) == 0:
start += 1
break
val = int(num[start:i+1])
dfs(num, i + 1, left_total + val, val, target, single + "+" + num[start:i+1], result)
dfs(num, i + 1, left_total - val, -val, target, single + "-" + num[start:i+1], result)
# back out the last val from left and get newly multiplied val*last and add it back to the left_total
dfs(num, i + 1, left_total - last + last * val, last * val, target, single + "*" + num[start:i+1], result)

result = []
start = 0
# you need this separate for loop for special handling the first operand.
for i in range(start, len(num)):
if i > 0 and int(num[:i+1]) == 0:
start += 1
break
val = int(num[:i+1])
dfs(num, i + 1, val, val, target, num[:i+1], result)
return result``````

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