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addOperators.py
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executable file
·56 lines (47 loc) · 1.71 KB
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"""
Given a string that contains only digits 0-9 and a target value, return
all possibilities to add binary operators (not unary) +, -, or * between
the digits so they evaluate to the target value.
Examples:
"123", 6 -> ["1+2+3", "1*2*3"]
"232", 8 -> ["2*3+2", "2+3*2"]
"105", 5 -> ["1*0+5","10-5"]
"00", 0 -> ["0+0", "0-0", "0*0"]
"3456237490", 9191 -> []
"""
class Solution:
def addOperators(self, num, target):
"""
:type num: str
:type target: int
:rtype: List[str]
"""
result, expr, val, i, valStr = [], [], 0, 0, ''
while i < len(num):
val = val * 10 + int(num[i])
valStr += num[i]
if str(val) != valStr: break
expr.append(valStr)
self.calc(num, target, i+1, 0, val, expr, result)
expr.pop()
i += 1
return result
def calc(self, num, target, pos, operand1, operand2, expr, result):
if pos == len(num) and operand1 + operand2 == target:
result.append(''.join(expr))
else:
val, i, valStr = 0, pos, ''
while i < len(num):
val = val * 10 + int(num[i])
valStr += num[i]
if str(val) != valStr: break
expr.append('+' + valStr)
self.calc(num, target, i+1, operand1+operand2, val, expr, result)
expr.pop()
expr.append('-' + valStr)
self.calc(num, target, i+1, operand1+operand2, -val, expr, result)
expr.pop()
expr.append('*' + valStr)
self.calc(num, target, i+1, operand1, operand2*val, expr, result)
expr.pop()
i += 1