code: func lastSequenceIndex(str string) int {
  	if len(str) == 0 {
  		return -1
  	}
  
  	if len(str) == 1 {
  		return 0
  	}
  
  	sequenceChar := str[0:1]
  	lastPos := 0
  	for i := 1; i < len(str); i++ {
  		if str[i:i+1] != sequenceChar {
  			break
  		}
  
  		lastPos = i
  	}
  
  	return lastPos
  }
docs: // lastSequenceIndex looks at the first character in a string and returns the
  // last digits of the first sequence of that character. For example:
  //  - ABC: 0
  //  - AAB: 1
  //  - ABA: 0
  //  - AAA: 2