二分法 binary_search

　　循环方式

const binarySearchByLoop = (arr = [0,1,2,3,4,5,6,7,8,9],target = 9) => {
    const { length } = arr
    let startIndex = 0
    let endIndex = length - 1
    while(startIndex <= endIndex){
        const midIndex = Math.floor((startIndex + endIndex) / 2)
        const value = arr[midIndex]
        if(value < target){
            startIndex = midIndex + 1
        }else if(value > target){
            endIndex = midIndex - 1
        }else{
            return midIndex
        }
    }
    return -1
}

　　递归方式

const binarySearchByRecursion = (arr = [0,1,2,3,4,5,6,7,8,9],target = 9, startIndex = 0,endIndex = arr.length - 1) => {
    if(startIndex > endIndex){
        return -1
    }
    const midIndex = Math.floor((startIndex + endIndex) / 2)
    const value = arr[midIndex]
    if(value < target){
        return binarySearchByRecursion(arr, target, midIndex + 1, endIndex)
    }else if(value > target){
        return binarySearchByRecursion(arr, target, startIndex, midIndex - 1)
    }else{
        return midIndex
    }
}