查找_在排序数组中查找数字|算法专题

        function binarySearch(data, arr, start, end) {
            if (start > end) {
                return -1;
            }
            var mid = Math.floor((end + start) / 2);
            if (data == arr[mid]) {
                return mid;
            } else if (data < arr[mid]) {
                return binarySearch(data, arr, start, mid - 1);
            } else {
                return binarySearch(data, arr, mid + 1, end);
            }
        }

    function GetNumberOfK(data, k) {
      if (data && data.length > 0 && k != null) {
        const firstIndex = getFirstK(data, 0, data.length - 1, k);
        const lastIndex = getLastK(data, 0, data.length - 1, k);
        if (firstIndex != -1 && lastIndex != -1) {
          return lastIndex - firstIndex + 1;
        }
      }
      return 0;
    }

    function getFirstK(data, first, last, k) {
      if (first > last) {
        return -1;
      }
      const mid = parseInt((first + last) / 2);
      if (data[mid] === k) {
        if (data[mid - 1] != k) {
          return mid;
        } else {
          return getFirstK(data, first, mid-1, k);
        }
      } else if (data[mid] > k) {
        return getFirstK(data, first, mid - 1, k);
      } else if (data[mid] < k) {
        return getFirstK(data, mid + 1, last, k);
      }
    }

    function getLastK(data, first, last, k) {
      if (first > last) {
        return -1;
      }
      const mid = parseInt((first + last) / 2);
      if (data[mid] === k) {
        if (data[mid + 1] != k) {
          return mid;
        } else {
          return getLastK(data, mid + 1, last, k);
        }
      } else if (data[mid] > k) {
        return getLastK(data, first, mid - 1, k);
      } else if (data[mid] < k) {
        return getLastK(data, mid + 1, last, k);
      }
    }