Create Expression Add Operators.py

Author: sugia

Expression Add Operators.py

@@ -0,0 +1,61 @@
+'''
+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.
+
+Example 1:
+
+Input: num = "123", target = 6
+Output: ["1+2+3", "1*2*3"] 
+
+Example 2:
+
+Input: num = "232", target = 8
+Output: ["2*3+2", "2+3*2"]
+
+Example 3:
+
+Input: num = "105", target = 5
+Output: ["1*0+5","10-5"]
+
+Example 4:
+
+Input: num = "00", target = 0
+Output: ["0+0", "0-0", "0*0"]
+
+Example 5:
+
+Input: num = "3456237490", target = 9191
+Output: []
+
+
+
+'''
+
+class Solution(object):
+    def addOperators(self, num, target):
+        """
+        :type num: str
+        :type target: int
+        :rtype: List[str]
+        """
+        res = []
+        if not num:
+            return res
+
+        for i in xrange(1, len(num)+1):
+            if i == 1 or (i > 1 and num[0] != '0'):
+                self.find(num[i:], int(num[:i]), target, num[:i], res, int(num[:i]))
+        
+        return res
+    
+    def find(self, num, tmpsum, target, tmp, res, last):
+        if not num:
+            if tmpsum == target:
+                res.append(tmp)
+            return
+        
+        for i in xrange(1, len(num)+1):
+            if i == 1 or (i > 1 and num[0] != '0'):
+                self.find(num[i:], tmpsum + int(num[:i]), target, tmp + '+' + num[:i], res, int(num[:i]))
+                self.find(num[i:], tmpsum - int(num[:i]), target, tmp + '-' + num[:i], res, -int(num[:i]))
+                self.find(num[i:], tmpsum - last + last * int(num[:i]), target, tmp + '*' + num[:i], res, last * int(num[:i]))
+