给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。

如果数组中不存在目标值 target，返回 [-1, -1]。

二分法

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class Solution {
    int[] searchRange(int[] nums, int target) {
        int leftBorder = getLeftBorder(nums, target);
        int rightBorder = getRightBorder(nums, target);
        // 情况一
        if (leftBorder == -2 || rightBorder == -2) {
        return new int[] {-1, -1};
        }
        // 情况三
        if (rightBorder - leftBorder > 1) {
        return new int[] {leftBorder+1,rightBorder - 1};
        }
        // 情况二
        return new int[] {-1, -1};
    }

    int getRightBorder(int[] nums, int target) {
        int left = 0;
        int right = nums.length - 1;
        int rightBorder = -2; 
        while (left <= right) {
            int middle = left + ((right - left) / 2);
            if (nums[middle] > target) {
                right = middle - 1;
            } else { 
                left = middle + 1;
                rightBorder = left;
            }
        }
        return rightBorder;
    }

    int getLeftBorder(int[] nums, int target) {
        int left = 0;
        int right = nums.length - 1;
        int leftBorder = -2; 
        while (left <= right) {
            int middle = left + ((right - left) / 2);
            if (nums[middle] >= target) { 
                right = middle - 1;
                leftBorder = right;
            } else {
                left = middle + 1;
            }
        }
        return leftBorder;
    }
}

双指针滑动窗口

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class Solution {
    public int[] searchRange(int[] nums, int target) {
        int i = 0;
        int k = 0;
        int j = 0;
        for (j = 0; j < nums.length; j++) {
            if(nums[j] == target) {
                k = 1;
                i = j++;
                while(j < nums.length && nums[j] == target) {
                    j++;
                }
                j--;
                break;
            }
        }
        if(k == 0) {
            int[] arr = {-1, -1};
        return arr;
        } else {
            int[] arr = {i, j};
            return arr;
        } 
    }
}

双指针滑动窗口易错点

越界可能 while(nums[j] == target)

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class Solution {
    public int[] searchRange(int[] nums, int target) {
        int i = 0;
        int k = 0;
        int j = 0;
        for (j = 0; j < nums.length; j++) {
            if(nums[j] == target) {
                k = 1;
                i = j++;
                while(nums[j] == target && j < nums.length) {
                    j++;
                }
                j--;
                break;
            }
        }
        if(k == 0) {
            int[] arr = {-1, -1};
        return arr;
        } else {
            int[] arr = {i, j};
            return arr;
        } 
    }
}