Combination Sum II
<p>Given a collection of candidate numbers (<code>candidates</code>) and a target number (<code>target</code>), find all unique combinations in <code>candidates</code>&nbsp;where the candidate numbers sum to <code>target</code>.</p>

<p>Each number in <code>candidates</code>&nbsp;may only be used <strong>once</strong> in the combination.</p>

<p><strong>Note:</strong>&nbsp;The solution set must not contain duplicate combinations.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> candidates = [10,1,2,7,6,1,5], target = 8
<strong>Output:</strong> 
[
[1,1,6],
[1,2,5],
[1,7],
[2,6]
]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> candidates = [2,5,2,1,2], target = 5
<strong>Output:</strong> 
[
[1,2,2],
[5]
]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;=&nbsp;candidates.length &lt;= 100</code></li>
	<li><code>1 &lt;=&nbsp;candidates[i] &lt;= 50</code></li>
	<li><code>1 &lt;= target &lt;= 30</code></li>
</ul>
Array; Backtracking
class Solution {
    /**
     * @param integer[] $candidates
     * @param integer $target
     * @return integer[][]
     */

    function combinationSum2($candidates, $target) {
        $result = [];
        $currentCombination = [];
        $startIndex = 0;

        sort($candidates);
        $this->findCombinations($candidates, $target, $startIndex, $currentCombination, $result);
        return $result;
    }

    function findCombinations($candidates, $target, $startIndex, $currentCombination, &$result) {
        if ($target === 0) {
            $result[] = $currentCombination;
            return;
        }

        for ($i = $startIndex; $i < count($candidates); $i++) {
            $num = $candidates[$i];
            if ($num > $target) {
                break;
            }

            if ($i > $startIndex && $candidates[$i] === $candidates[$i - 1]) {
                continue;
            }
            $currentCombination[] = $num;

            $this->findCombinations($candidates, $target - $num, $i + 1, $currentCombination, $result);
            array_pop($currentCombination);
        }
    }
}
