src/main/java/com/leetcode/design/easy/ImplementQueueUsingStacks_232.java
public void push(int x) {
      if (stack.isEmpty()) {
        front = x;
      }
      stack.push(x);
    }
/** Push element x to the back of queue. */
Push element x to the back of queue.
Push element x to the back of queue .
public void push(int x) {
      if (stack.isEmpty()) {
        front = x;
      }
      stack.push(x);
    }
public void push ( int x ) { if ( stack . isEmpty ( ) ) { front = x ; } stack . push ( x ) ; }
Push element x to the back of queue.
Push element x to the back of queue .