Merge pull request #2 from darwinz/binary-search

Binary search algorithm - iterative and recursive

.gitignore

@@ -0,0 +1,5 @@
+.idea
+.vscode
+.phan
+vendor
+composer.lock

composer.json

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+{
+    "require-dev": {
+    },
+    "require": {
+        "phan/phan": "^2.7"
+    }
+}

searches/binary_search.php

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+<?php
+function binarySearchIterative($list, $target)
+{
+  /*
+   * Binary search algorithm in PHP
+   *
+   * Be careful collection must be ascending sorted, otherwise result will be unpredictable
+   *
+   * @param Array $list a sorted array list of integers to search
+   * @param integer $target an integer number to search for in the list
+   * @return integer the index where the target is found (or null if not found)
+   *
+   * Examples:
+   * binarySearchIterative([0, 5, 7, 10, 15], 0);
+   * 0
+   * binarySearchIterative([0, 5, 7, 10, 15], 15);
+   * 4
+   * binarySearchIterative([0, 5, 7, 10, 15], 5);
+   * 1
+   * binarySearchIterative([0, 5, 7, 10, 15], 6);
+   *
+   */
+    $first = 0;
+    $last = count($list)-1;
+
+
+    while ($first <= $last) {
+        $mid = ($first + $last) >> 1;
+
+
+        if ($list[$mid] == $target) {
+            return $mid;
+        } elseif ($list[$mid] > $target) {
+            $last = $mid - 1;
+        } elseif ($list[$mid] < $target) {
+            $first = $mid + 1;
+        }
+    }
+
+    return null;
+}
+
+function binarySearchByRecursion($list, $target, $start, $end)
+{
+  /*
+   * Binary search algorithm in PHP by recursion
+   *
+   * Be careful collection must be ascending sorted, otherwise result will be unpredictable
+   *
+   * @param Array $list a sorted array list of integers to search
+   * @param integer $target an integer number to search for in the list
+   * @param integer $start an integer number where to start searching in the list
+   * @param integer $end an integer number where to end searching in the list
+   * @return integer the index where the target is found (or null if not found)
+   *
+   * Examples:
+   * binarySearchByRecursion([0, 5, 7, 10, 15], 0, 0, 4);
+   * 0
+   * binarySearchByRecursion([0, 5, 7, 10, 15], 15, 0, 4);
+   * 4
+   * binarySearchByRecursion([0, 5, 7, 10, 15], 5, 0, 4);
+   * 1
+   * binarySearchByRecursion([0, 5, 7, 10, 15], 6, 0, 4);
+   *
+   */
+    if ($start > $end)
+        return null;
+
+
+    $mid = ($start + $end) >> 1;
+
+
+    if ($list[$mid] == $target) {
+        return $mid;
+    } elseif ($list[$mid] > $target) {
+        return binarySearchByRecursion($list, $target, $start, $mid-1);
+    } elseif ($list[$mid] < $target) {
+        return binarySearchByRecursion($list, $target, $mid+1, $end);
+    }
+
+    return null;
+}
+
+
+assert(binarySearchIterative([0, 5, 7, 10, 15], 0) == 0);
+assert(binarySearchIterative([0, 5, 7, 10, 15], 7) == 2);
+assert(binarySearchIterative([0, 5, 7, 10, 15], 8) == null);
+
+assert(binarySearchByRecursion([0, 5, 7, 10, 15], 0, 0, 4) == 0);
+assert(binarySearchByRecursion([0, 5, 7, 10, 15], 15, 0, 4) == 4);
+assert(binarySearchByRecursion([0, 5, 7, 10, 15], 7, 0, 4) == 2);
+assert(binarySearchByRecursion([0, 5, 7, 10, 15], 6, 0, 4) == null);