ios - 获取 3 个有序值的数组，同时支持指定值

Question

抱歉，标题有点笼统，如果有人有更好的建议，请告诉我。

基本上我正在编写一个自定义排行榜视图，我只想显示 3 个分数。如果可能，它将在中间显示当前用户的分数，但如果用户位于列表的顶部或底部，它仍应显示 3 个分数，但它会在列表上方或下方显示其他用户。

例如

1. 我（如果我名列前茅，请在下面显示 2）
2. 用户 1
3. 用户 2

或者

1. 用户 1
2. 我（通常情况下我处于两个分数的中间）
3. 用户 2

或者

1. 用户 1
2. 用户 2
3. 我（如果我垫底，显示比我高两个分数）

我编写了一个函数来完成第一部分，但没有考虑到我正在努力解决的边缘情况。有人可以请教吗？

-(void)getNearbyScores:(int)score{
    GCLeaderboardScore *closestScoreAbove = nil; //Custom container for GC properties
    GCLeaderboardScore *closestScoreBelow = nil; //Contains playerID, score, alias etc

    if ([playerScores count] == 0){ //playerScores is an NSMutableDictionary
        return;
    }

    for (NSString* key in playerScores) {

        GCLeaderboardScore *playerScore = (GCLeaderboardScore *)[playerScores objectForKey:key];
        if ((closestScoreAbove == nil || closestScoreAbove->score > playerScore->score)  && playerScore->score > score){
            closestScoreAbove = playerScore;
        }
        else if ((closestScoreBelow == nil || closestScoreAbove->score < playerScore->score) && playerScore->score < score){
            closestScoreBelow = playerScore;
        }
    }

    me->score = score;
    me->rank = 1;
    if (closestScoreAbove != nil) {
        me->rank = closestScoreAbove->rank + 1;
        nearbyScores = [NSMutableArray arrayWithObjects: closestScoreAbove, me, closestScoreBelow, nil];
    }
    else {
        nearbyScores = [NSMutableArray arrayWithObjects: me, closestScoreBelow, nil];
    }
}

Answer 1

假设有一个me GCLeaderboardScore对象，下面的方法应该返回一个包含所需GCLeaderboardScore对象的数组（未经测试）：

-(NSArray *)getNearbyScores {

    if(playerScores.count==0) return nil;

    // Create an array sorted by score
    NSArray *sortedByScore=[playerScores sortedArrayUsingComparator: ^(id object1, id object2) {
        GCLeaderboardScore  *score1=object1;
        GCLeaderboardScore  *score2=object2;

        if(score1->score < score2->score) return NSOrderedAscending;
        if(score1->score > score2->score) return NSOrderedDescending;

        return NSOrderedSame;
    }];

    // Find index of me
    NSUInteger  idx=[sortedByScore indexOfObject:me];

    // If me not found, return nil
    if(idx==NSNotFound) return nil;

    // Ideally we want to show the player before and behind
    idx=MAX(0,(NSInteger)idx-1);

    // maxIdx will be idx+2 or index of last object if lower
    NSUInteger  maxIdx=MIN(sortedByScore.count-1,idx+2);

    // In case we are last, show two previous results (if array large enough)
    if (maxIdx > 3)
                idx=MAX(0,maxIdx-3);

    // And return the objects, may be 1..3 objects
    return [sortedByScore subarrayWithRange:NSMakeRange(idx,maxIdx-idx+1)];
}

Answer 2

我假设你有一系列分数。（实际实现可以适应你的代码）

Initialize:  
firstScoreAbove = VERY_LARGE_SCORE; secondScoreAbove = VERY_LARGE_SCORE + 1;
firstScoreBelow = -1; secondScoreBelow = -2;

Scan the array elements.
if ( newScore > myScore ) {
  if ( newScore < firstScoreAbove ) {
     secondScoreAbove = firstScoreAbove;
     firstScoreAbove = newScore;
  } else if ( newScore < secondScoreAbove ) {
     secondScoreAbove = newScore;
  }
} else {
  // similarly for below.
}

扫描后，
如果 firstScoreAbove 没有变化，则 myScore 为 top 并输出以下两个分数。
如果 firstScoreBelow 没有变化，则 myScore 最低，输出以上两个分数。
否则输出 firstScoreAbove、myScore、firstScoreBelow。