二分查找

    function binarySearch(array, value) {
        let low = 0,
            high = array.length - 1;
        while (low <= high) {
            let mid = (low + high) / 2;
            if (value === array[mid]) {
                return mid;
            } else if (value < array[mid]) {
                high = mid - 1;
            } else if (value > array[mid]) {
                low = mid + 1;
            }
        }
        console.log('值不存在');
        return undefined;
    }

重写

查找前需要排序

function binarySearch(arr,value){
    if(arr.length === 0) return null
    let bottom = 0,
        top = arr.length - 1
    while(bottom<=top){
        let index = Math.floor((bottom+top)/2)
        if(arr[index] === value){
            return index
        }else if(arr[index]>value){
            top = index - 1
        }else if(arr[index]<value){
            bottom = index + 1
        }
    }
    return null
}