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3.7: Sequential Search

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  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    The next method we’ll write is search, which takes an array of cards and a Card object as parameters. It returns the index where the Card appears in the array, or -1 if it doesn’t. This version of search uses the algorithm we saw in Section 8.6, which is called sequential search:

    public static int search(Card[] cards, Card target) {
        for (int i = 0; i < cards.length; i++) {
            if (cards[i].equals(target)) {
                return i;
        return -1;

    The method returns as soon as it discovers the card, which means we don’t have to traverse the entire array if we find the target. If we get to the end of the loop, we know the card is not in the array. Notice that this algorithm depends on the equals method.

    If the cards in the array are not in order, there is no way to search faster than sequential search. We have to look at every card, because otherwise we can’t be certain the card we want is not there. But if the cards are in order, we can use better algorithms.

    We will learn in the next chapter how to sort arrays. If you pay the price to keep them sorted, finding elements becomes much easier. Especially for large arrays, sequential search is rather inefficient.

    This page titled 3.7: Sequential Search is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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