二分查找

/**
 * @Classname BinarySearch
 * @Description 二分查找（前提：数组有序）
 * @Date 2021/2/26 23:00
 * @Created by 12345678
 */
public class BinarySearch {
    public static void main(String[] args) {
        int[] arr = {1, 1, 1, 4, 6, 8, 9};
        int[] arr1 = {1, 3, 5, 6};
        ArrayList<Integer> list = binarySerach(arr, 0, arr.length - 1, 1);
        binarySerach(arr1, 0, arr1.length - 1, 1);
        if (list.size() == 0) System.out.println("-1");
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }


    }

    public static ArrayList<Integer> binarySerach(int[] arr, int left, int right, int findVal) {
        if (left > right) {
            //通过判断是否为空决定是否找到
            return new ArrayList<>();
        }
        int mid = (left + right) / 2;
        int midVal = arr[mid];
        if (findVal > midVal) {
            return binarySerach(arr, mid + 1, right, findVal);
        } else if (findVal < midVal) {
            return binarySerach(arr, left, mid - 1, findVal);
        } else {
            //找到了则向前 向后查找是否存在相同的值 全部加入list中
            ArrayList<Integer> indexList = new ArrayList<>();
            int temp = mid - 1;
            //向左找
            while (true) {
                if (temp < 0 || arr[temp] != findVal) {
                    break;
                }
                indexList.add(temp);
                //注意：temp左移
                temp -= 1;
            }
            indexList.add(mid);
            //向右找
            temp = mid + 1;
            while (true) {
                if (temp > arr.length - 1 || arr[temp] != findVal) {
                    break;
                }
                indexList.add(temp);
                temp += 1;
            }
            return indexList;
        }
    }
}

标签：二分,arr,indexList,temp,int,findVal,mid,查找
来源： https://blog.csdn.net/qq_42349617/article/details/114160910