lastoccurrence

Last occurrence is a concept in computer science and data processing that refers to the final position at which a given value, character, substring, or pattern appears within a sequence. It is commonly applied to strings and arrays, where the goal is to locate the rightmost match rather than the first one.

In practice, last occurrence searches are used to determine where something happens last in a data set. For example, finding the last index of a character in a string, or locating the last occurrence of a substring within a larger text. This information is useful for parsing, data extraction, and cleaning tasks, as well as for algorithms that need to understand the tail behavior of data.

Computing the last occurrence is typically done by scanning the sequence from the end toward the beginning and stopping when a match is found. This yields a time complexity of O(n) in the worst case, where n is the length of the sequence. Many programming languages provide built-in facilities for this operation, such as rfind or lastIndexOf, which implement the right-to-left search and return the index of the last match or a sentinel value (for example, -1 or nil) if no match exists.

Edge cases include situations where the value or pattern does not occur at all, the sequence is empty, or range-limited searches are requested (for instance, within a specific portion of the sequence). Variants distinguish between last occurrences of a single character, a substring, or a more complex pattern, and whether the search is case-sensitive.

See also: rightmost occurrence, lastIndexOf, rfind, string search.