//time:O(nlgn)

//space:O(n)

class Solution {

public String[] reorderLogFiles(String[] logs) {

Arrays.sort(logs, (s1, s2) -> { // Array.sort(logs,0,5) index 0 included,index 5 excluded.

String[] split1 = s1.split(" ", 2); // split by " ".

String[] split2 = s2.split(" ", 2);

boolean isDigit1 = Character.isDigit(split1[1].charAt(0));

boolean isDigit2 = Character.isDigit(split2[1].charAt(0));

if(!isDigit1 && !isDigit2) {

// both letter-logs.

int comp = split1[1].compareTo(split2[1]);

if (comp == 0) return split1[0].compareTo(split2[0]);

else return comp;

} else if (isDigit1 && isDigit2) {

// both digit-logs. So keep them in original order

return 0;

} else if (isDigit1 && !isDigit2) {

// first is digit, second is letter. bring letter to forward.

return 1;

} else {

//first is letter, second is digit. keep them in this order.

return -1;

}

});

return logs;

}

}