Expression Add Operators(leetcode)

Expression Add Operators

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题目

leetcode题目
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 -> []

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解决

class Solution {public:    void addOperator(vector<string> & result, string nums, string r, long long last, long long current, int target) {        if (nums.length() == 0) {            if (current == target) {                result.push_back(r);            }            return;        }        for (int i = 1; i <= nums.length(); i++) {            string num = nums.substr(0, i);            if (num.length() >= 2 && num[0] == '0') {                return;            }            string next = nums.substr(i);            if (r.length() > 0) {                addOperator(result, next, r + "+" + num, stoll(num), current + stoll(num), target);                addOperator(result, next, r + "-" + num, -stoll(num), current - stoll(num), target);                addOperator(result, next, r + "*" + num, last * stoll(num), (current - last) + (last * stoll(num)), target);            } else {                addOperator(result, next, num, stoll(num), stoll(num), target);            }        }    }    vector<string> addOperators(string num, int target) {        vector<string> result;        addOperator(result, num, "", 0, 0, target);        return result;    }};