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leetcode/divide-and-conquer/ExpressionAddOperators.java
47 строк
2 KB
Kevin Naughton Jr
finish renaming files and directories
27 мар 2018, 19:52
27 мар 2018, 19:52
ec6dfb5
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// 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 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) { result.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(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); } } } }