package org.lza;

//import java.util.Stack;

/*
 * Given an input string, reverse the string word by word.
 * For example,
 * Given s = "the sky is blue",
 * return "blue is sky the".
 */
/*
 * 思路：首先 看到題目中只是單詞被反序 單詞內部沒有反序 想到反序可以用棧來實現
 */
public class ReverseString {
 public static void main(String[] args) {
  String s = "the sky is blue";
  String reversStr = Reverse(s);
  System.out.println(reversStr);
 }

 public static String Reverse(String s) {
  // 建立一個空棧
  int length = s.length();
  Stack stack = new Stack();
  char[] str = s.toCharArray();
  // char[] strRs=new char[length];
  StringBuffer strRs = new StringBuffer();
  for (char ch : str) {
   stack.push(ch);// 入棧
  }
  Stack stackTemp = new Stack();
  int j = -1;
  for (int i = 0; i < length; i++) {
   if (stack.isEmpty())
    break;
   char ch = (char) stack.pop();
   if (ch != ' ') { // 將單詞字母入棧
    stackTemp.push(ch);
    if(!stack.isEmpty())
     continue;
   }
   if (!stackTemp.isEmpty()) {// 碰到空字元或者棧底則反轉單詞
    while(!stackTemp.isEmpty())
     // strRs[n]=(char)stackTemp.pop();
     strRs.append(stackTemp.pop());
    j = i;
   }
   if(ch==' ')
    strRs.append(ch);
  }
  return strRs.toString();
 }
}

class Stack {
 private final int LEN = 10;// 初始棧大小
 private int top;// 棧頂指標
 private Object[] elements;// 資料元素陣列

 public Stack() { // 初始化棧
  top = -1;
  elements = new Object[LEN];
 }
 /*
  * 函式名：isEmpty()
  * @return:棧為空則返回true，否則返回false
  */
 public boolean isEmpty() {
  return top < 0;
 }
 /*
  * 函式名：public void push(Object e)
  * 函式功能：將元素插入棧中
  * @param Object e:要進棧的元素
  * @return :無
  */
 public void push(Object e){
  if(elements.length+1>=LEN){
   //擴充儲存空間
   expandStack();
  }
  elements[++top]=e;
  
 }
 private void expandStack(){
  Object[] temp=new Object[elements.length*2];
  for(int i=0;i<elements.length;i++){
   temp[i]=elements[i];
  }
  elements=temp;
 }
 public int getSize(){
  return top+1;
 }
 public Object pop(){
  if(getSize()<1){
   System.out.println("空棧！");
   return null;
  }
  Object e=elements[top];
  elements[top--]=null;//釋放記憶體
  return e;
 }
}