PHP implementation of classic algorithms, 300 classic examples of PHP programming, classic examples of PHP recursive algorithms, PHP classic interviews-PHP Tutorial-php.cn

Foreword

The following is a classic algorithm implemented through PHP, and the time consumption is calculated. The complexity of these algorithms can be compared by the time consumption.

Insertion sort
Bubble sort
Selection sort
Merge sort
Quick sort

CODE

<code><span>$arr</span> = [];

<span>for</span> (<span>$i</span> = <span>0</span>; <span>$i</span> < <span>5000</span>; <span>$i</span>++) {
    <span>$arr</span>[] = rand(<span>1</span>, <span>10000</span>);
}


<span>//1 插入排序</span><span><span>function</span><span>insertionSort</span><span>(<span>$arr</span>)</span>
{</span><span>for</span> (<span>$i</span> = <span>1</span>; <span>$i</span> < count(<span>$arr</span>); <span>$i</span>++) {
        <span>$tmp</span> = <span>$arr</span>[<span>$i</span>]; <span>//设置监视哨</span><span>$key</span> = <span>$i</span> - <span>1</span>; <span>//设置开始查找的位置</span><span>while</span> (<span>$key</span> >= <span>0</span> && <span>$tmp</span> < <span>$arr</span>[<span>$key</span>]) { <span>// 监视哨的值比查找的值小 并且 没有到此次查询的第一个</span><span>$arr</span>[<span>$key</span> + <span>1</span>] = <span>$arr</span>[<span>$key</span>];  <span>//数组的值进行后移</span><span>$key</span>--;  <span>//要查找的位置后移</span>
        }
        <span>if</span> ((<span>$key</span> + <span>1</span>) != <span>$i</span>) <span>//放置监视哨</span><span>$arr</span>[<span>$key</span> + <span>1</span>] = <span>$tmp</span>;
    }
    <span>return</span><span>$arr</span>;

}

<span>$insertion_start_time</span> = microtime(<span>true</span>);

<span>$insertion_sort</span> = insertionSort(<span>$arr</span>);

<span>$insertion_end_time</span> = microtime(<span>true</span>);

<span>$insertion_need_time</span> = <span>$insertion_end_time</span> - <span>$insertion_start_time</span>;

print_r(<span>"插入排序耗时:"</span> . <span>$insertion_need_time</span> . <span>"<br />");


<span>//2 冒泡排序</span><span><span>function</span><span>bubbleSort</span><span>(<span>$arr</span>)</span>
{</span><span>for</span> (<span>$i</span> = <span>0</span>; <span>$i</span> < count(<span>$arr</span>); <span>$i</span>++) {
        <span>for</span> (<span>$j</span> = <span>0</span>; <span>$j</span> < <span>$i</span> + <span>1</span>; <span>$j</span>++) {
            <span>if</span> (<span>$arr</span>[<span>$j</span>] < <span>$arr</span>[<span>$j</span> - <span>1</span>]) {
                <span>$temp</span> = <span>$arr</span>[<span>$j</span> - <span>1</span>];
                <span>$arr</span>[<span>$j</span> - <span>1</span>] = <span>$arr</span>[<span>$j</span>];
                <span>$arr</span>[<span>$j</span>] = <span>$temp</span>;

            }
        }
    }
    <span>return</span><span>$arr</span>;
}

<span>$bubble_start_time</span> = microtime(<span>true</span>);

<span>$bubble_sort</span> = bubbleSort(<span>$arr</span>);

<span>$bubble_end_time</span> = microtime(<span>true</span>);

<span>$bubble_need_time</span> = <span>$bubble_end_time</span> - <span>$bubble_start_time</span>;

print_r(<span>"冒泡排序耗时:"</span> . <span>$bubble_need_time</span> . <span>"<br />");

<span>//3 选择排序</span><span><span>function</span><span>selectionSort</span><span>(<span>$arr</span>)</span>
{</span><span>$count</span> = count(<span>$arr</span>);
    <span>for</span> (<span>$i</span> = <span>0</span>; <span>$i</span> < <span>$count</span> - <span>1</span>; <span>$i</span>++) {
        <span>//找到最小的值</span><span>$min</span> = <span>$i</span>;
        <span>for</span> (<span>$j</span> = <span>$i</span> + <span>1</span>; <span>$j</span> < <span>$count</span>; <span>$j</span>++) {
            <span>//由小到大排列</span><span>if</span> (<span>$arr</span>[<span>$min</span>] > <span>$arr</span>[<span>$j</span>]) {
                <span>//表明当前最小的还比当前的元素大</span><span>$min</span> = <span>$j</span>;
                <span>//赋值新的最小的</span>
            }
        }
        <span>/*swap$array[$i]and$array[$min]即将当前内循环的最小元素放在$i位置上*/</span><span>if</span> (<span>$min</span> != <span>$i</span>) {
            <span>$temp</span> = <span>$arr</span>[<span>$min</span>];
            <span>$arr</span>[<span>$min</span>] = <span>$arr</span>[<span>$i</span>];
            <span>$arr</span>[<span>$i</span>] = <span>$temp</span>;
        }
    }
    <span>return</span><span>$arr</span>;

}

<span>$selection_start_time</span> = microtime(<span>true</span>);

<span>$selection_sort</span> = selectionSort(<span>$arr</span>);

<span>$selection_end_time</span> = microtime(<span>true</span>);

<span>$selection_need_time</span> = <span>$selection_end_time</span> - <span>$selection_start_time</span>;

print_r(<span>"选择排序耗时:"</span> . <span>$selection_need_time</span> . <span>"<br />"</span>);

<span>//4 并归排序</span><span>//merge函数将指定的两个有序数组(arr1arr2,)合并并且排序</span><span>//我们可以找到第三个数组,然后依次从两个数组的开始取数据哪个数据小就先取哪个的,然后删除掉刚刚取过///的数据</span><span><span>function</span><span>al_merge</span><span>(<span>$arrA</span>, <span>$arrB</span>)</span>
{</span><span>$arrC</span> = <span>array</span>();
    <span>while</span> (count(<span>$arrA</span>) && count(<span>$arrB</span>)) {
        <span>//这里不断的判断哪个值小,就将小的值给到arrC,但是到最后肯定要剩下几个值,</span><span>//不是剩下arrA里面的就是剩下arrB里面的而且这几个有序的值,肯定比arrC里面所有的值都大所以使用</span><span>$arrC</span>[] = <span>$arrA</span>[<span>'0'</span>] < <span>$arrB</span>[<span>'0'</span>] ? array_shift(<span>$arrA</span>) : array_shift(<span>$arrB</span>);
    }
    <span>return</span> array_merge(<span>$arrC</span>, <span>$arrA</span>, <span>$arrB</span>);
}

<span>//归并排序主程序</span><span><span>function</span><span>al_merge_sort</span><span>(<span>$arr</span>)</span>
{</span><span>$len</span> = count(<span>$arr</span>);
    <span>if</span> (<span>$len</span> <= <span>1</span>)
        <span>return</span><span>$arr</span>;<span>//递归结束条件,到达这步的时候,数组就只剩下一个元素了,也就是分离了数组</span><span>$mid</span> = intval(<span>$len</span> / <span>2</span>);<span>//取数组中间</span><span>$left_arr</span> = array_slice(<span>$arr</span>, <span>0</span>, <span>$mid</span>);<span>//拆分数组0-mid这部分给左边left_arr</span><span>$right_arr</span> = array_slice(<span>$arr</span>, <span>$mid</span>);<span>//拆分数组mid-末尾这部分给右边right_arr</span><span>$left_arr</span> = al_merge_sort(<span>$left_arr</span>);<span>//左边拆分完后开始递归合并往上走</span><span>$right_arr</span> = al_merge_sort(<span>$right_arr</span>);<span>//右边拆分完毕开始递归往上走</span><span>$arr</span> = al_merge(<span>$left_arr</span>, <span>$right_arr</span>);<span>//合并两个数组,继续递归</span><span>return</span><span>$arr</span>;
}

<span>$merge_start_time</span> = microtime(<span>true</span>);

<span>$merge_sort</span> = al_merge_sort(<span>$arr</span>);

<span>$merge_end_time</span> = microtime(<span>true</span>);

<span>$merge_need_time</span> = <span>$merge_end_time</span> - <span>$merge_start_time</span>;

print_r(<span>"并归排序耗时:"</span> . <span>$merge_need_time</span> . <span>"<br />"</span>);

<span>//5 快速排序</span><span><span>function</span><span>quickSort</span><span>(&<span>$arr</span>)</span>{</span><span>if</span>(count(<span>$arr</span>)><span>1</span>){
        <span>$k</span>=<span>$arr</span>[<span>0</span>];
        <span>$x</span>=<span>array</span>();
        <span>$y</span>=<span>array</span>();
        <span>$_size</span>=count(<span>$arr</span>);
        <span>for</span>(<span>$i</span>=<span>1</span>;<span>$i</span><<span>$_size</span>;<span>$i</span>++){
            <span>if</span>(<span>$arr</span>[<span>$i</span>]<=<span>$k</span>){
                <span>$x</span>[]=<span>$arr</span>[<span>$i</span>];
            }<span>elseif</span>(<span>$arr</span>[<span>$i</span>]><span>$k</span>){
                <span>$y</span>[]=<span>$arr</span>[<span>$i</span>];
            }
        }
        <span>$x</span>=quickSort(<span>$x</span>);
        <span>$y</span>=quickSort(<span>$y</span>);
        <span>return</span> array_merge(<span>$x</span>,<span>array</span>(<span>$k</span>),<span>$y</span>);
    }<span>else</span>{
        <span>return</span><span>$arr</span>;
    }
}

<span>$quick_start_time</span> = microtime(<span>true</span>);

<span>$quick_sort</span> = al_merge_sort(<span>$arr</span>);

<span>$quick_end_time</span> = microtime(<span>true</span>);

<span>$quick_need_time</span> = <span>$quick_end_time</span> - <span>$quick_start_time</span>;

print_r(<span>"快速排序耗时:"</span> . <span>$quick_need_time</span> . <span>"<br />"</span>);

</code>

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Time-consuming comparison

Insertion sort time-consuming: 1.2335460186005
Bubble sorting time: 2.6180219650269
Selection sorting time: 1.4159741401672
Merge sorting time: 0.17212891578674
Quick sort takes time: 0.16736888885498

References

Introduction to Algorithms

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