g1701_1800.s1759_count_number_of_homogenous_substrings.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g1701_1800.s1759_count_number_of_homogenous_substrings;

// #Medium #String #Math #2022_04_30_Time_19_ms_(42.40%)_Space_51.3_MB_(28.80%)

/**
 * 1759 - Count Number of Homogenous Substrings\.
 *
 * Medium
 *
 * Given a string `s`, return _the number of **homogenous** substrings of_ `s`_._ Since the answer may be too large, return it **modulo** 10⁹ + 7.
 *
 * A string is **homogenous** if all the characters of the string are the same.
 *
 * A **substring** is a contiguous sequence of characters within a string.
 *
 * **Example 1:**
 *
 * **Input:** s = "abbcccaa"
 *
 * **Output:** 13
 *
 * **Explanation:** The homogenous substrings are listed as below: 
 *
 * "a" appears 3 times. 
 *
 * "aa" appears 1 time. 
 *
 * "b" appears 2 times. 
 *
 * "bb" appears 1 time. 
 *
 * "c" appears 3 times. 
 *
 * "cc" appears 2 times. 
 *
 * "ccc" appears 1 time. 
 *
 * 3 + 1 + 2 + 1 + 3 + 2 + 1 = 13.
 *
 * **Example 2:**
 *
 * **Input:** s = "xy"
 *
 * **Output:** 2
 *
 * **Explanation:** The homogenous substrings are "x" and "y".
 *
 * **Example 3:**
 *
 * **Input:** s = "zzzzz"
 *
 * **Output:** 15
 *
 * **Constraints:**
 *
 * *   1 <= s.length <= 10⁵
 * *   `s` consists of lowercase letters.
**/
public class Solution {
    public int countHomogenous(String s) {
        int total = 0;
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            if (i > 0 && s.charAt(i) == s.charAt(i - 1)) {
                count++;
            } else {
                count = 1;
            }
            total = (total + count) % 1000000007;
        }
        return total;
    }
}