282. Expression Add Operators
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 -> []
1 class Solution { 2 public: 3 vector<string> addOperators(string num, int target) { 4 5 vector<string> res; 6 if (num.size() == 0) 7 return res; 8 9 DFS(num, target, 0, "", res, 0, 0); 10 return res; 11 } 12 13 void DFS(string& num, int& target, int cur, string path, 14 vector<string>& res, long long diff, long long sum) { 15 16 if (cur == int(num.size()) && sum == target) { 17 res.push_back(path); 18 return; 19 } 20 for (size_t i = cur; i < num.size(); i++) { 21 string curStr = num.substr(cur, i - cur + 1); 22 if (curStr.size() > 1 && curStr[0] == '0') 23 return; 24 long curVal = atol(curStr.c_str()); 25 if (cur > 0) { 26 DFS(num, target, i + 1, path + '+' + curStr, res, curVal, 27 sum + curVal); 28 DFS(num, target, i + 1, path + '-' + curStr, res, -curVal, 29 sum - curVal); 30 DFS(num, target, i + 1, path + '*' + curStr, res, diff * curVal, 31 sum - diff + diff * curVal); 32 } else { 33 DFS(num, target, i + 1, path + curStr, res, curVal, 34 sum + curVal); 35 } 36 } 37 38 } 39 };
