剑指offer-问题38

package offer;

/**
 * offer interview 38
 */
public class Test38 {

    private static int getFirstK(int[] data,int k,int start,int end){
        if (data == null || data.length < 1 || start > end){
            return -1;
        }

        int midIdx = start + (end - start) / 2;
        int midData = data[midIdx];

        if (midData == k){
            if (midIdx > 0 && data[midIdx - 1] != k || midIdx == 0){
                return midIdx;
            }else{
                end = midIdx - 1;
            }
        }else if (midData > k){
            end = midIdx - 1;
        }else{
            start = midIdx + 1;
        }

        return getFirstK(data,k,start,end);
    }

    private static int getLastK(int[] data,int k,int start,int end){
        if (data == null || data.length < 1 || start > end){
            return -1;
        }

        int midIdx = start + (end - start) / 2;
        int midData = data[midIdx];

        if (midData == k ){
            if (midIdx + 1 < data.length && data[midIdx + 1] != k || midIdx == data.length - 1 ){
                return midIdx;
            }else{
                start = midIdx + 1;
            }
        }else if(midData < k){
             start = midIdx + 1;
        }else{
            end = midIdx - 1;
        }

        return getLastK(data,k,start,end);
    }


    public static int getNumberOfK(int[] data , int k){
        int number = 0;
        if (data != null && data.length > 0){
            int first = getFirstK(data,k,0,data.length - 1);
            int last = getLastK(data,k,0,data.length -1 );

            if (first > -1 && last > -1){
                number = last - first + 1;
            }
        }

        return number;
    }


    public static void main(String[] args){
        int[] data1 = {1, 2, 3, 3, 3, 3, 4, 5};
        System.out.println(getNumberOfK(data1,3));

        // 查找的数组出现在数组的开头
        int[] data2 = {3, 3, 3, 3, 4, 5};
        System.out.println(getNumberOfK(data2, 3)); // 4

        // 查找的数组出现在数组的结尾
        int[] data3 = {1, 2, 3, 3, 3, 3};
        System.out.println(getNumberOfK(data3, 3)); // 4

        // 查找的数字不存在
        int[] data4 = {1, 3, 3, 3, 3, 4, 5};
        System.out.println(getNumberOfK(data4, 2)); // 0

        // 查找的数字比第一个数字还小，不存在
        int[] data5 = {1, 3, 3, 3, 3, 4, 5};
        System.out.println(getNumberOfK(data5, 0)); // 0

        // 查找的数字比最后一个数字还大，不存在
        int[] data6 = {1, 3, 3, 3, 3, 4, 5};
        System.out.println(getNumberOfK(data6, 0)); // 0

        // 数组中的数字从头到尾都是查找的数字
        int[] data7 = {3, 3, 3, 3};
        System.out.println(getNumberOfK(data7, 3)); // 4

        // 数组中的数字从头到尾只有一个重复的数字，不是查找的数字
        int[] data8 = {3, 3, 3, 3};
        System.out.println(getNumberOfK(data8, 4)); // 0

        // 数组中只有一个数字，是查找的数字
        int[] data9 = {3};
        System.out.println(getNumberOfK(data9, 3)); // 1

        // 数组中只有一个数字，不是查找的数字
        int[] data10 = {3};
        System.out.println(getNumberOfK(data10, 4)); // 0
    }
}

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