PHP实现的回溯算法示例

<?php
/
  k = 2x + y + 1/2z
 取值范围
  0 <= x <= 1/2k
  0 <= y <= k
  0 <= z < = 2k
  x,y,z最大值 2k
 /
$daMi = 100;
$result = array();
function isOk($t,$daMi,$result)
{/{{{/
 $total = 0;
 $hash = array();
 $hash[1] = 2;
 $hash[2] = 1;
 $hash[3] = 0.5;
 for($i=1;$i<=$t;$i++)
 {
 $total += $result[$i]  $hash[$i];
 }
 if( $total <= $daMi)
 {
 return true;
 }
 return false;
}/}}}/
function backtrack($t,$daMi,$result)
{/{{{/
 //递归出口
 if($t > 3)
 {
 //输出最优解
 if($daMi == (2  $result[1] + $result[2] + 0.5  $result[3]))
 {
  echo "最优解，大米:${daMi},大牛$result[1],中牛 $result[2]，小牛$result[3]\n";
 }
 return;
 }
 for($i = 0;$i <= 2  $daMi;$i++)
 {
 $result[$t] = $i;
 //剪枝
 if(isOk($t,$daMi,$result))
 {
  backtrack($t+1,$daMi,$result);
 }
 $result[$t] = 0;
 }
}/}}}/
backtrack(1,$daMi,$result);
?>