Problem
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.
Example 1:
Input: num = "123", target = 6
Output: ["1+2+3", "123"]
Example 2:
Input: num = "232", target = 8
Output: ["23+2", "2+32"]
Example 3:
Input: num = "105", target = 5
Output: ["1*0+5","10-5"]
Example 4:
Input: num = "00", target = 0
Output: ["0+0", "0-0", "0*0"]
Example 5:
Input: num = "3456237490", target = 9191
Output: []
class Solution { public ListSave path to StringBuilderaddOperators(String num, int target) { List res = new ArrayList<>(); if (num == null || num.length() == 0) return res; dfs(num, "", 0, target, res, 0, 0); return res; } private void dfs(String num, String temp, int index, int target, List res, long val, long multi) { if (index == num.length()) { if (val == target) res.add(temp); return; } for (int i = index; i < num.length(); i++) { if (i != index && num.charAt(index) == "0") break; long cur = Long.parseLong(num.substring(index, i+1)); if (index == 0) { dfs(num, temp+cur, i+1, target, res, cur, cur); } else { dfs(num, temp+"+"+cur, i+1, target, res, val+cur, cur); dfs(num, temp+"-"+cur, i+1, target, res, val-cur, -cur); dfs(num, temp+"*"+cur, i+1, target, res, val-multi+multi*cur, multi*cur); } } } }
class Solution { public ListUse char[] to store num and use StringBuilderaddOperators(String num, int target) { List res = new ArrayList<>(); dfs(num, 0, 0, target, 0, new StringBuilder(), res); return res; } private void dfs(String num, int index, long value, int target, long multi, StringBuilder sb, List res) { if (index == num.length()) { if (value == target) res.add(sb.toString()); return; } for (int i = index; i < num.length(); i++) { if (num.charAt(index) == "0" && i != index) break; long cur = Long.parseLong(num.substring(index, i+1)); int len = sb.length(); if (index == 0) { sb.append(cur); dfs(num, i+1, cur, target, cur, sb, res); sb.setLength(len); } else { sb.append("+").append(cur); dfs(num, i+1, value+cur, target, cur, sb, res); sb.setLength(len); sb.append("-").append(cur); dfs(num, i+1, value-cur, target, -cur, sb, res); sb.setLength(len); sb.append("*").append(cur); dfs(num, i+1, value-multi+multi*cur, target, multi*cur, sb, res); sb.setLength(len); } } } }
class Solution { public ListaddOperators(String num, int target) { List res = new ArrayList<>(); dfs(num.toCharArray(), 0, new StringBuilder(), 0, 0, target, res); return res; } private void dfs(char[] digits, int index, StringBuilder sb, long value, long multi, int target, List res) { if (index == digits.length) { if (value == target) res.add(sb.toString()); return; } for (int i = index; i < digits.length; i++) { if (digits[index] == "0" && i != index) break; long cur = Long.parseLong(new String(digits, index, i-index+1)); int len = sb.length(); if (index == 0) { sb.append(cur); dfs(digits, i+1, sb, cur, cur, target, res); sb.setLength(len); } else { sb.append("+").append(cur); dfs(digits, i+1, sb, value+cur, cur, target, res); sb.setLength(len); sb.append("-").append(cur); dfs(digits, i+1, sb, value-cur, -cur, target, res); sb.setLength(len); sb.append("*").append(cur); dfs(digits, i+1, sb, value-multi+multi*cur, multi*cur, target, res); sb.setLength(len); } } } }
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