# Expression Add Operators

Expression Add Operators and conquer

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 -> []
``````

Expression Add Operators Solution

``````public class ExpressionAddOperators {
public List<String> addOperators(String num, int target) {
List<String> result = new ArrayList<String>();

if(num == null || num.length() == 0) {
return result;
}

helper(result, "", num, target, 0, 0, 0);
return result;
}

public void helper(List<String> result, String path, String num, int target, int pos, long eval, long multed) {
if(pos == num.length()) {
if(eval == target) {
}

return;
}

for(int i = pos; i < num.length(); i++) {
if(i != pos && num.charAt(pos) == '0') {
break;
}

long cur = Long.parseLong(num.substring(pos, i + 1));

if(pos == 0) {
helper(result, path + cur, num, target, i + 1, cur, cur);
} else {
helper(result, path + "+" + cur, num, target, i + 1, eval + cur, cur);
helper(result, path + "-" + cur, num, target, i + 1, eval - cur, -cur);
helper(result, path + "*" + cur, num, target, i + 1, eval - multed + multed * cur, multed * cur);
}
}
}
}``````