[leetcode]Basic Calculator II

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public class Solution { public int calculate(String s) { s = s.replaceAll(" ", ""); List<String> list = new LinkedList<String>(); String prev = ""; int i = 0; while(i<s.length()){ char current = s.charAt(i); if (current == '*' || current == '/'){ int numberEnd = nextNumberRange(s, i+1); int op2 = Integer.valueOf(s.substring(i+1, numberEnd)); list.add(doMath(current, Integer.valueOf(list.remove(list.size()-1)), op2)+""); i = numberEnd; }else if (current == '+' || current == '-'){ list.add(current+""); i++; }else{ int numberEnd = nextNumberRange(s, i); list.add(s.substring(i, numberEnd)); i = numberEnd; } } if (list.isEmpty()) return 0; while (list.size()!=1){ int op1 = Integer.valueOf(list.remove(0)); char op = list.remove(0).charAt(0); int op2 = Integer.valueOf(list.remove(0)); list.add(0,doMath(op, op1, op2)+""); } return Integer.valueOf(list.remove(0)); } private int doMath(char op, int op1, int op2){ if (op == '*') return op1*op2; if (op == '/') return op1/op2; if (op == '-') return op1-op2; return op1+op2; } private int nextNumberRange(String s, int starting){ while (starting < s.length()){ char current = s.charAt(starting); if (current == '*' || current == '/' ||current == '-' || current == '+'){ return starting; } starting++; } return starting; } }