算法 查找

   查找⽐较简单，我们先来看⼀个经典的⼆分查找 有点类似幸运52的猜价格，⽐如让你在1和1000之间猜个数字，挨个猜是很蠢的，要先猜500，如果⼤了，那就是0~500 ，每次问题减半，很快就能查到

function binarySeatch(arr,target) {
    var low=0,
        high=arr.length-1,
        mid;
    while(low<=high){
        mid=Math.floor((low+high)/2);
        if(target===arr[mid]){
            return `找到了${target},在第${mid + 1}个`
        }
        if(target>arr[mid]){
            low=mid+1;
        }else if(target<arr[mid]){
            high=mid-1
        }
    }
    return  -1
}

console.log(binarySeatch([1,2,3,4,5,6],2))

function binarySearch1(arr,target,low=0,high=arr.length-1) {

    const n=Math.floor((low+high)/2);
    const cur=arr[n];
    if(cur===target){
        return `找到了${target},在第${mid + 1}个`
    }else if(cur>target){
        return binarySearch1(arr,target,low,n-1)
    }else if(cur<target){
        return binarySearch1(arr,target,n+1,high)
    }
    return -1
}