pythonCode.py

class Solution:
    def addOperators(self, num: str, target: int):
        def backTrack(index, pre, cur, value, s):
            if index == n:
                if value == target and cur == 0:
                    ans.append(s)
                return
            cur = cur * 10 + int(num[index])
            if cur > 0:
                backTrack(index+1, pre, cur, value, s)
            if not s:
                backTrack(index+1, cur, 0, value+cur, str(cur))
            else:
                backTrack(index+1, cur, 0, value+cur, s+'+'+str(cur))
                backTrack(index+1, -cur, 0, value-cur, s+'-'+str(cur))
                backTrack(index+1, pre*cur, 0, value-pre+pre*cur, s+'*'+str(cur))
        n = len(num)
        ans = []
        backTrack(0, 0, 0, 0, "")
        return ans