js实现抽奖概率

// 定义奖品和对应的概率
const prizes = [
  { name: '一等奖', probability: 0.1 },
  { name: '二等奖', probability: 0.2 },
  { name: '三等奖', probability: 0.3 },
  { name: '谢谢参与', probability: 0.4 }
];

// 计算总概率
const totalProbability = prizes.reduce((sum, prize) => sum + prize.probability, 0);

// 抽奖函数
function drawPrize() {
  const randomNum = Math.random() * totalProbability;
  let cumulativeProbability = 0;

  for (const prize of prizes) {
    cumulativeProbability += prize.probability;
    if (randomNum < cumulativeProbability) {
      return prize.name;
    }
  }

  // 如果由于浮点数精度问题没有匹配到，返回最后一个奖品
  return prizes[prizes.length - 1].name;
}

// 测试抽奖函数
console.log(drawPrize());

function drawPrizeOptimized() {
  const randomNum = Math.random() * totalProbability;
  let left = 0;
  let right = prizes.length - 1;

  while (left < right) {
    const mid = Math.floor((left + right) / 2);
    cumulativeProbability = prizes.slice(0, mid + 1).reduce((sum, prize) => sum + prize.probability, 0);
    if (randomNum < cumulativeProbability) {
      right = mid;
    } else {
      left = mid + 1;
    }
  }

  return prizes[left].name;
}

// 测试优化后的抽奖函数
console.log(drawPrizeOptimized());