AMIDA.php

<?php
$inputData = explode(' ', fgets(STDIN));

$depthLength = $inputData[0];
$countPosition = $inputData[1];
$maxMove = $inputData[2];

$moves = [];
for($i=1; $i<=$maxMove; $i++){
    $eachData = explode(' ', fgets(STDIN));
    $moves[] = [
        'position' => $eachData[0],
        'startDepth' => $eachData[1],
        'endDepth' => $eachData[2],
    ];
}

$currentPosition = 1;
$currentDepth = 0;
$prevPosition = 0;
$prevDepth = 0;
while(1==1){
    if($prevPosition != $currentPosition or $prevDepth != $currentDepth){
        list($currentPosition, $currentDepth) = move($currentPosition, $currentDepth, $moves, $countPosition);
    }else{
        break;
    }
    $prevPosition = $currentPosition;
    $prevDepth = $currentDepth;
}

echo $currentPosition;

function move($position, $depth, $moves, $countPosition){
    //右行きで一番近い線
    if($position <$countPosition){
    $rightMove = [];
    $minRightBetween = 10000;
        foreach($moves as $move){
            if($move['position'] == $position && $move['startDepth'] > $depth){
                if($minRightBetween > ($move['startDepth'] - $depth)){
                   $minRightBetween = $move['startDepth'] - $depth;
                   $rightMove = $move;
                }
            }
        }
    }else{
        $minRightBetween = 10000;

    }

    //左行きで一番近い線
    if($position > 0){
        $leftMove = [];
        $minLeftBetween = 10000;
        foreach($moves as $move){
            if(($move['position'] + 1)  == $position && $move['endDepth'] > $depth){
                if($minLeftBetween > ($move['endDepth'] - $depth)){
                   $minLeftBetween = $move['endDepth'] - $depth;
                   $leftMove = $move;
                }
            }
        }
    }else{
        $minLeftBetween = 10000;
    }
    
    if(!isset($rightMove['position']) && !isset($leftMove['position'])){
        return [$position, $depth];
    }
    
    if($minRightBetween <= $minLeftBetween){
        return [$rightMove['position'], $rightMove['endDepth']];
    }else{
        return [$leftMove['position'], $leftMove['startDepth']];
        
    }
}

?>