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 -> []
public class Solution { public List<String> addOperators(String num, int target) { List<String> res = new ArrayList<String>(); if(num == null || num.length() == 0) return res; helper(num, target, res, "", 0, 0, 0); return res; } public void helper(String num, int target, List<String> res, String path, int pos, long eval, long mul) { if (pos == num.length()) { if (eval == target) { res.add(path); 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(num, target, res, path+cur, i+1, cur, cur); else { helper(num, target, res, path+"+"+cur, i+1, eval+cur, cur); helper(num, target, res, path+"-"+cur, i+1, eval-cur, -cur); helper(num, target, res, path+"*"+cur, i+1, eval-mul+mul*cur, cur*mul); } } }}新闻热点
疑难解答
