Substring With Largest Variance.java

class Solution {
  public int largestVariance(String s) {
    int ans = 0;
    for (char c1 = 'a'; c1 <= 'z'; ++c1)
      for (char c2 = 'a'; c2 <= 'z'; ++c2)
        if (c1 != c2)
          ans = Math.max(ans, kadane(s, c1, c2));
    return ans;
  }
  private int kadane(final String s, char a, char b) {
    int ans = 0;
    int countA = 0;
    int countB = 0;
    boolean canExtendPrevB = false;
    for (final char c : s.toCharArray()) {
      if (c != a && c != b)
        continue;
      if (c == a)
        ++countA;
      else
        ++countB;
      if (countB > 0) {
        ans = Math.max(ans, countA - countB);
      } else if (countB == 0 && canExtendPrevB) {
        ans = Math.max(ans, countA - 1);
      }
      if (countB > countA) {
        countA = 0;
        countB = 0;
        canExtendPrevB = true;
      }
    }
    return ans;
  }
}