code: func (c *configuration) lc(k, cnt head) head {
  	if k < 0 || int(k) > c.N() {
  		return DOES_NOT_EXIST
  	}
  
  	cc := 0
  	for i := 1; i < int(k); i++ {
  		if c.Head(i) == int(k) {
  			cc++
  			if int(cnt) == cc {
  				return head(i)
  			}
  		}
  	}
  	return DOES_NOT_EXIST
  }
docs: // gets the jth left child of the ith word of a sentence