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nsun9505 solved 수식 최대화
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‎Programmers/[2020 카카오 인턴십] 수식 최대화/nsun9505/java/README.md‎

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# [2020 카카오 인턴십] 수식 최대화 - JAVA
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## 분류
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> 스택
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>
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> 순열
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## 코드
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```java
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.Stack;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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public class Solution {
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static HashMap<String, Integer> opMap = new HashMap<>();
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static Stack<String> stack = new Stack<>();
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static ArrayList<String> list = new ArrayList<>();
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static ArrayList<String> exp = new ArrayList<>();
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static String[] operators;
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static long ans = 0;
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public long solution(String expression) {
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Pattern pattern = Pattern.compile("\\d{1,3}");
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Matcher matcher = pattern.matcher(expression);
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while(matcher.find())
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list.add(matcher.group());
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pattern = Pattern.compile("\\D");
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matcher = pattern.matcher(expression);
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HashSet<String> opSet = new HashSet<>();
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int idx = 0;
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while(matcher.find()) {
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String op = matcher.group();
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opSet.add(op);
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exp.add(list.get(idx++));
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exp.add(op);
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}
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exp.add(list.get(idx));
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operators = new String[opSet.size()];
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idx = 0;
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for(String op : opSet)
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operators[idx++] = op;
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perm(0);
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return ans;
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}
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public void perm(int depth){
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if(depth == operators.length){
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for(int i=0; i<operators.length; i++)
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opMap.put(operators[i], i);
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list.clear();
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stack.clear();
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for(int i=0; i<exp.size(); i++){
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String str = exp.get(i);
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if(str.equals("+") || str.equals("-") || str.equals("/") || str.equals("*")){
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while(!stack.isEmpty()){
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if(opMap.get(stack.peek()) < opMap.get(str))
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break;
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list.add(stack.pop());
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}
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stack.push(str);
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} else {
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list.add(str);
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}
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}
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while(!stack.isEmpty())
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list.add(stack.pop());
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for(String str : list){
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if(str.equals("+") || str.equals("-") || str.equals("/") || str.equals("*")){
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long op2 = Long.parseLong(stack.pop());
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long op1 = Long.parseLong(stack.pop());
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if(str.equals("+"))
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stack.push(String.valueOf(op1 + op2));
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else if(str.equals("-"))
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stack.push(String.valueOf(op1 - op2));
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else if(str.equals("*"))
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stack.push(String.valueOf(op1 * op2));
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else
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stack.push(String.valueOf(op1 / op2));
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} else {
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stack.push(str);
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}
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}
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long sum = Math.abs(Long.parseLong(stack.pop()));
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ans = Math.max(ans, sum);
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return;
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}
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for(int i=depth; i<operators.length; i++){
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swap(depth, i);
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perm(depth+1);
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swap(depth, i);
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}
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}
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public void swap(int x, int y){
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String tmp = operators[x];
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operators[x] = operators[y];
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operators[y] = tmp;
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}
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}
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```
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## 문제 풀이
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먼저 연산자와 피연산자를 알아오기 위해서 정규 표현식을 사용해서 파싱했습니다.
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- "\\d" : 숫자만 가져오기
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- "\\D" : 숫자가 아닌 애들 가져오기
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순열을 사용해서 연산자의 순서를 정하고 정해진 순서에 따라 Map에 우선순위를 저장하였습니다.
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계산하는 방법은 중위 표현식을 후위표현식으로 변경하여 계산하였습니다.
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## 후기
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후위 표현식과 순열을 사용하면 쉽게 풀 수 있는 문제였습니다!
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후위 표현식은 코드 안 보고 짜봤습니다!
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싸피가 도움이 되긴 하네요..ㅎ

‎Programmers/[2020 카카오 인턴십] 수식 최대화/nsun9505/java/Solution.java‎

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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.Stack;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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public class Solution {
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static HashMap<String, Integer> opMap = new HashMap<>();
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static Stack<String> stack = new Stack<>();
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static ArrayList<String> list = new ArrayList<>();
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static ArrayList<String> exp = new ArrayList<>();
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static String[] operators;
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static long ans = 0;
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public long solution(String expression) {
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Pattern pattern = Pattern.compile("\\d{1,3}");
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Matcher matcher = pattern.matcher(expression);
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while(matcher.find())
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list.add(matcher.group());
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pattern = Pattern.compile("\\D");
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matcher = pattern.matcher(expression);
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HashSet<String> opSet = new HashSet<>();
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int idx = 0;
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while(matcher.find()) {
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String op = matcher.group();
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opSet.add(op);
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exp.add(list.get(idx++));
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exp.add(op);
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}
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exp.add(list.get(idx));
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operators = new String[opSet.size()];
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idx = 0;
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for(String op : opSet)
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operators[idx++] = op;
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perm(0);
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return ans;
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}
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public void perm(int depth){
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if(depth == operators.length){
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for(int i=0; i<operators.length; i++)
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opMap.put(operators[i], i);
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list.clear();
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stack.clear();
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for(int i=0; i<exp.size(); i++){
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String str = exp.get(i);
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if(str.equals("+") || str.equals("-") || str.equals("/") || str.equals("*")){
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while(!stack.isEmpty()){
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if(opMap.get(stack.peek()) < opMap.get(str))
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break;
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list.add(stack.pop());
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}
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stack.push(str);
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} else {
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list.add(str);
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}
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}
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while(!stack.isEmpty())
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list.add(stack.pop());
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for(String str : list){
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if(str.equals("+") || str.equals("-") || str.equals("/") || str.equals("*")){
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long op2 = Long.parseLong(stack.pop());
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long op1 = Long.parseLong(stack.pop());
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if(str.equals("+"))
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stack.push(String.valueOf(op1 + op2));
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else if(str.equals("-"))
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stack.push(String.valueOf(op1 - op2));
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else if(str.equals("*"))
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stack.push(String.valueOf(op1 * op2));
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else
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stack.push(String.valueOf(op1 / op2));
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} else {
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stack.push(str);
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}
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}
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long sum = Math.abs(Long.parseLong(stack.pop()));
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ans = Math.max(ans, sum);
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return;
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}
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for(int i=depth; i<operators.length; i++){
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swap(depth, i);
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perm(depth+1);
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swap(depth, i);
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}
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}
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public void swap(int x, int y){
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String tmp = operators[x];
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operators[x] = operators[y];
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operators[y] = tmp;
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}
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}

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