Horace7：static String removeParentheses(String input){ int length = input.length(); char[] array = input.toCharArray(); int count = 0; Stack<Integer> parenthesesStack = new Stack<>(); StringBuilder sb = new StringBuilder(); for (int i=0; i< length; i++){ switch (array[i]){ case '-': sb.append(((count&1) == 1)?'+':'-'); if(i < length - 1 && array[i+1] == '('){ count ++; parenthesesStack.push(i+1); i++; } break; case ')': int lastLeftIndex = parenthesesStack.pop(); if (lastLeftIndex > 0 && array[lastLeftIndex - 1] == '-') { count--; } break; case '+': sb.append(((count&1) == 1)?'-':'+'); break; case '(': parenthesesStack.push(i); break; default: sb.append(array[i]); } } return sb.toString(); }