js实现一个权重抽奖

权重抽奖实现方法

权重抽奖的核心是根据不同奖项的权重值随机抽取一个奖项。以下是使用JavaScript实现的几种方法：

方法一：基于数组和随机数

1. 准备奖项及其权重数组

   const prizes = [
   { name: '一等奖', weight: 10 },
   { name: '二等奖', weight: 20 },
   { name: '三等奖', weight: 30 },
   { name: '参与奖', weight: 40 }
   ];

2. 计算总权重并生成随机数

   
   function weightedRandom(prizes) {
   const totalWeight = prizes.reduce((sum, prize) => sum + prize.weight, 0);
   const random = Math.random() * totalWeight;

let currentWeight = 0; for (const prize of prizes) { currentWeight += prize.weight; if (random <= currentWeight) { return prize; } }

return prizes[prizes.length - 1]; // 默认返回最后一个 }

#### 方法二：使用概率分布

1. 预处理权重为累积概率
```javascript
function prepareWeights(prizes) {
  const totalWeight = prizes.reduce((sum, prize) => sum + prize.weight, 0);
  let cumulativeWeight = 0;

  return prizes.map(prize => {
    cumulativeWeight += prize.weight;
    return {
      ...prize,
      cumulativeWeight,
      probability: prize.weight / totalWeight
    };
  });
}

1. 执行抽奖

   
   function drawPrize(preparedPrizes) {
   const random = Math.random() * preparedPrizes[preparedPrizes.length - 1].cumulativeWeight;

return preparedPrizes.find(prize => random <= prize.cumulativeWeight) || preparedPrizes[preparedPrizes.length - 1]; }

#### 方法三：优化版（适合大量奖项）

1. 使用二分查找提高效率
```javascript
function weightedRandomBinarySearch(prizes) {
  const cumulativeWeights = [];
  let sum = 0;

  for (const prize of prizes) {
    sum += prize.weight;
    cumulativeWeights.push(sum);
  }

  const random = Math.random() * sum;
  let left = 0;
  let right = cumulativeWeights.length - 1;

  while (left < right) {
    const mid = Math.floor((left + right) / 2);
    if (random > cumulativeWeights[mid]) {
      left = mid + 1;
    } else {
      right = mid;
    }
  }

  return prizes[left];
}

使用示例

const preparedPrizes = prepareWeights(prizes);
const result = drawPrize(preparedPrizes);
console.log(`恭喜获得：${result.name}`);

注意事项

• 权重值可以是任意正数，不限于百分比
• 确保权重总和不为零
• 对于高频抽奖场景，建议预处理权重数据
• 可根据需要添加奖项抽空后的处理逻辑

这些方法可根据实际需求进行调整，比如添加抽奖次数限制、奖项库存控制等功能。