418. Sentence Screen Fitting

Given a rows x cols screen and a sentence represented by a list of non-empty words, find how many times the given sentence can be fitted on the screen.

Note:

A word cannot be split into two lines.
The order of words in the sentence must remain unchanged.
Two consecutive words in a line must be separated by a single space.
Total words in the sentence won't exceed 100.
Length of each word is greater than 0 and won't exceed 10.
1 ≤ rows, cols ≤ 20,000.
Example 1:

Input:
rows = 2, cols = 8, sentence = ["hello", "world"]

Output:
1

Explanation:
hello---
world---

The character '-' signifies an empty space on the screen.
Example 2:

Input:
rows = 3, cols = 6, sentence = ["a", "bcd", "e"]

Output:
2

Explanation:
a-bcd-
e-a---
bcd-e-

The character '-' signifies an empty space on the screen.
Example 3:

Input:
rows = 4, cols = 5, sentence = ["I", "had", "apple", "pie"]

Output:
1

Explanation:
I-had
apple
pie-I
had--

The character '-' signifies an empty space on the screen.

Solution

repeat s to form one line text
use start to record the index every row starts with
* Consider transformation of start

Reference: https://leetcode.com/problems/sentence-screen-fitting/discuss/90845/21ms-18-lines-Java-solution

Complexity

Worst O(rows * cols)
O(1)

Code

class Solution {
    public int wordsTyping(String[] sentence, int rows, int cols) {
        String s = String.join(" ", sentence) + " ";
        int start = 0, l = s.length();
        
        for(int i =0; i < rows; ++i){
            start += cols;
            if(s.charAt(start % l) == ' '){
                start++;
            }else{
                while(start > 0 && s.charAt((start-1) % l) != ' ') 
                    start--;
            }
        }
        return start/l;
    }
}