二分法查找

用二分法查找数组中某一个元素的下标。ps:二分法查找只适用于有序数组

二分法原理图(来源网络):

int[] arr  = new int[]{1,2,3,4,5,6,7,8,9,10};

public int binarySearch(int value){
    int middle = 0;//中间索引值
    int low = 0;
    int high = arr.length - 1;
    while(low <= high){
        middle = (high+low)/2;
        if(arr[middle]==value){
            return middle;
        }
        if(arr[middle] > value){//中间值比较大，往左边找
            high  = middle - 1;
        }else{//往右边找
            low = middle + 1;
        }
    }
    return -1;
}

调用

binarySearch(8);

结果是7