Find Number Combinations in PHP

What You’ll Learn

“Number combinations” in beginner exercises usually means nested-loop index patterns: every ordering of three values, then every unordered pair from a longer list. This tutorial covers permutations vs combinations, distinct-index rules, a live preview, worked PHP examples, edge cases, and complexity.

📝 Problem & Approach

Store numbers in an array, then visit valid index tuples with nested for loops and print each result.

// [1, 2, 3] orderings -> 6 lines (permutations)
// [10, 20, 30, 40] pairs -> 6 lines (C(4, 2))

Inputs & Outputs

Minimal workflow

// All orderings of three array entries (indices 0..2)
for i in 0..2:
  for j in 0..2:
    for k in 0..2:
      if i, j, k all different:
        print arr[i], arr[j], arr[k]

// All unordered pairs from indices 0..n-1
for i in 0..n-2:
  for j in i+1 .. n-1:
    print arr[i], arr[j]

Method comparison

🔮 Live Preview

Enter three integers separated by commas (same as Example 1: 1, 2, 3). Shows all six orderings when indices are distinct.

Press “List orderings”.

Examples Gallery

Three complete PHP programs — permutations of three numbers, unordered pairs from four, and ordered pairs. Click View Output to reveal sample console results.

<?php
$arr = [1, 2, 3];

echo "All orderings (permutations) of the three numbers:\n";

for ($i = 0; $i < 3; $i++) {
    for ($j = 0; $j < 3; $j++) {
        for ($k = 0; $k < 3; $k++) {
            if ($i !== $j && $j !== $k && $i !== $k) {
                echo $arr[$i] . " " . $arr[$j] . " " . $arr[$k] . "\n";
            }
        }
    }
}
?>

All orderings (permutations) of the three numbers:
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

<?php
$arr = [10, 20, 30, 40];
$n = count($arr);

echo "All unordered pairs (choose 2 from $n):\n";

for ($i = 0; $i < $n; $i++) {
    for ($j = $i + 1; $j < $n; $j++) {
        echo $arr[$i] . " " . $arr[$j] . "\n";
    }
}
?>

All unordered pairs (choose 2 from 4):
10 20
10 30
10 40
20 30
20 40
30 40

<?php
$arr = [10, 20, 30, 40];
$n = count($arr);

echo "All ordered pairs (i != j):\n";

for ($i = 0; $i < $n; $i++) {
    for ($j = 0; $j < $n; $j++) {
        if ($i !== $j) {
            echo $arr[$i] . " " . $arr[$j] . "\n";
        }
    }
}
?>

All ordered pairs (i != j):
10 20
10 30
10 40
20 10
20 30
20 40
30 10
30 20
30 40
40 10
40 20
40 30

🔎 Worked Walkthrough — Pairs from [10, 20, 30, 40]

Trace Example 2: outer $i, then $j from $i + 1.

Total: 3 + 2 + 1 = 6 = C(4, 2).

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

For general triples from n elements, expect O(n³) if you scan all index triples.

💡 Best Practices