LintCode 14: First Position of Target

博客围绕在给定的升序排序数组中查找目标数的首个索引展开,要求时间复杂度为O(log n),若目标数不存在则返回 -1。给出了多个示例,还提出若数组元素数量大于2^32代码能否正常工作的挑战,并给出了类似二分查找的解法。

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  1. First Position of Target
    中文English
    For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity.

If the target number does not exist in the array, return -1.

Example
Example 1:
Input: [1,4,4,5,7,7,8,9,9,10],1
Output: 0

Explanation: 
the first index of  1 is 0.

Example 2:
Input: [1, 2, 3, 3, 4, 5, 10],3
Output: 2

Explanation: 
the first index of 3 is 2.

Example 3:
Input: [1, 2, 3, 3, 4, 5, 10],6
Output: -1

Explanation: 
Not exist 6 in array.

Challenge
If the count of numbers is bigger than 2^32, can your code work properly?

解法1:类似Binary Search。
代码如下:

class Solution {
public:
    /**
     * @param nums: The integer array.
     * @param target: Target to find.
     * @return: The first position of target. Position starts from 0.
     */
    int binarySearch(vector<int> &nums, int target) {
        int n = nums.size();
        if (n == 0) return -1;
        
        int start = 0, end = n - 1;
        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (nums[mid] < target) {
                start = mid;
            } else if (nums[mid] >= target) {
                end = mid;
            }
        }
        
        if (nums[start] == target) return start;
        if (nums[end] == target) return end;
        return -1;
    }
};
:first-child和:first-of-type是CSS选择器中的两个不同的选择器。 :first-child选择器匹配其父元素中的第一个子元素。例如,如果我们有以下CSS代码: p:first-child { background-color: yellow; } span:first-child { background-color: yellow; } 那么它将选择所有p元素和span元素中的第一个子元素,并将其背景颜色设置为黄色。\[1\] :first-of-type选择器匹配其父级是特定类型的第一个子元素。例如,如果我们有以下CSS代码: p:first-of-type { color: blue; } 那么它将选择所有p元素中的第一个子元素,并将其字体颜色设置为蓝色。注意,这里的:first-of-type只要是该类型元素的第一个就行了,不要求是第一个子元素了。\[2\] 所以,两个选择器的区别在于:first-child选择器只匹配其父元素中的第一个子元素,而:first-of-type选择器匹配其父级是特定类型的第一个子元素。 #### 引用[.reference_title] - *1* [css:first-child和first-of-type](https://blog.youkuaiyun.com/xiaojinguniang/article/details/119887850)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item] - *2* [:first-child和:first-of-type的区别](https://blog.youkuaiyun.com/weixin_46305214/article/details/104644576)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item] - *3* [CSS选择器 :first-of-type/:last-of-type/ :first-child/:last-child 用法](https://blog.youkuaiyun.com/momo_mom177/article/details/124008659)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item] [ .reference_list ]
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