34. Find First and Last Position of Element in Sorted Array

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int startIndex = findStartIndex(nums, target);
        if (startIndex == -1) {
            return new int[]{-1, -1};
        } else {
            return new int[]{startIndex, findEndIndex(nums, target)};
        }
    }

    private int findEndIndex(int[] nums, int target) {
        int left = 0, right = nums.length - 1; // [left, right]
        while (left <= right) {
            int mid = (left + right) >>> 1;
            if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }

        // now: right, left
        if (right == -1 || nums[right] != target) {
            return -1;
        }

        return right;
    }

    private int findStartIndex(int[] nums, int target) {
        int left = 0, right = nums.length - 1; // [left, right]
        while (left <= right) {
            int mid = (left + right) >>> 1;
            if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid - 1;
            } else {
                right = mid - 1;
            }
        }

        // now: right, left
        if (left == nums.length || nums[left] != target) {
            return -1;
        }

        return left;
    }
}

注意此题是搜索第一个和最后一个位置而不是搜索插入位置，所以需要比较最后停留的位置的值是否为目标值。

Reference