src/main/java/org/wltea/analyzer/core/QuickSortSet.java
Lexeme pollLast(){
		if(this.size == 1){
			Lexeme last = this.head.lexeme;
			this.head = null;
			this.tail = null;
			this.size--;
			return last;
			
		}else if(this.size > 1){
			Lexeme last = this.tail.lexeme;
			this.tail = this.tail.prev;
			this.size--;
			return last;
			
		}else{
			return null;
		}
	}
Lexeme pollLast(){
		if(this.size == 1){
			Lexeme last = this.head.lexeme;
			this.head = null;
			this.tail = null;
			this.size--;
			return last;
			
		}else if(this.size > 1){
			Lexeme last = this.tail.lexeme;
			this.tail = this.tail.prev;
			this.size--;
			return last;
			
		}else{
			return null;
		}
	}
取出链表集合的最后一个元素
@return Lexeme