[LeetCode] Expression Add Operators

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This post shares a very nice solution, which is rewritten below.

 1 class Solution { 2 public: 3     vector<string> addOperators(string num, int target) { 4         int n = num.length(); 5         if (!n) return {}; 6         vector<string> ans; 7         for (int i = 1; i <= n; i++) { 8             string s = num.substr(0, i); 9             long v = stol(s);10             if (s != to_string(v)) continue;11             add(ans, num, target, s, i, v, v, ‘$‘);12         }13         return ans;14     }15 private:16     void add(vector<string>& ans, string& num, int target, string s, int i, long v, long pv, char op) {17         int n = num.length();18         if (i == n && v == target)19             ans.push_back(s);20         else {21             for (int p = i + 1; p <= n; p++) {22                 string t = num.substr(i, p - i);23                 long d = stol(t);24                 if (t != to_string(d)) continue;25                 add(ans, num, target, s + ‘+‘ + t, p, v + d, d, ‘+‘);26                 add(ans, num, target, s + ‘-‘ + t, p, v - d, d, ‘-‘);27                 add(ans, num, target, s + ‘*‘ + t, p, (op == ‘+‘) ? v - pv + pv * d : ((op == ‘-‘) ? v + pv - pv * d: pv * d), pv * d, op);28             }29         }30     }31 };

 

[LeetCode] Expression Add Operators