Last Substring in Lexicographical Order LeetCode solution in JavaScript

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// Second Solution
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// Efficient
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/*
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The substring starting with the largest character is the answer. Hence we advance j and try to find the biggest character 
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while we use i to keep track of the current maximum string.
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What if there is more than one largest character?
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- we will need to compare both substrings starting with the largest character.
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- (1) the substring with bigger next character is the answer.
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- (2) if the shorter substring is exactly the same to the longer substring up to its end, the longer substring is the answer.
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i is the starting index of the answer
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j is the pointer iterating through given string
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k is the offset to use when we find two substrings starting with the same character
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*/
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var lastSubstring = function (s) {
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  let i = 0,
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    j = 1,
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    k = 0;
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  while (j + k < s.length) {
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    k = 0;
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    while (s[i + k] === s[j + k]) {
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      k += 1;
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      if (j + k === s.length) break;
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      // if the shorter substring is exactly the same to the longer substring up to its end,
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      // the longer substring is the answer.
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      // hence, if j+k reaches the end, s.substring(i) will be the answer since we maintain i < j
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    }
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    if (s[i + k] > s[j + k]) {
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      j = j + 1 + k; // because there is no chance s[i+k] <= s[j+k]
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    } else if (s[i + k] < s[j + k]) {
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      i = i + 1 + k; // because there is no chance s[i+k] >= s[j+k]
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    }
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    // to ensure that i < j
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    if (i >= j) {
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      j = i + 1;
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    }
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  }
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  return s.substring(i);
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  // T.C: O(N)
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  // S.C: O(1)
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};