代码随想录算法训练营第一天|704.二分查找、35.搜索插入的位置、34.在排序数组中查找元素的第一个和最后一个位置、27.移除元素

704.二分查找

题目链接：https://leetcode.cn/problems/binary-search/

//开区间写法
class Solution {
public:
    int search(vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size();
        int mid;
        while(l<r){
            mid = l + r >> 1;
            if(nums[mid] == target) return mid;
            else if(nums[mid] > target) r = mid;
            else l = mid + 1;
        }
        return -1;
    }
};

//闭区间写法
class Solution {
public:
    int search(vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size() - 1;
        int mid;
        while(l<=r){
            mid = l + r >> 1;
            if(nums[mid] == target) return mid;
            else if(nums[mid] > target) r = mid - 1;
            else l = mid + 1;
        }
        return -1;
    }
};

35.搜索插入的位置

题目链接：https://leetcode.cn/problems/search-insert-position/description/

//闭区间
class Solution {
public:
    int searchInsert(vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size() - 1;
        int mid;
        while(l<=r){
            mid = l + r >> 1;
            if(nums[mid] == target) return mid;
            if(nums[mid] < target) l = mid + 1;
            else r = mid - 1;
        }
        return l;
    }
}

//开区间
class Solution {
public:
    int searchInsert(vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size();
        int mid;
        while(l < r){
            mid = l + r >> 1;
            if(nums[mid] == target) return mid;
            if(nums[mid] < target) l = mid + 1;
            else r = mid;
        }
        return l;
    }
};

34.在排序数组中查找元素的第一个和最后一个位置

题目链接：https://leetcode.cn/problems/find-first-and-last-position-of-element-in-sorted-array/

class Solution {
public:
    int lower_bound(vector<int> &nums,int target){
        int l = 0;
        int r = nums.size() - 1;
        while(l < r){
            int mid = (l + r) / 2;
            if(nums[mid] == target) r = mid;
            else if(nums[mid] < target) l = mid + 1;
            else r = mid - 1;
        }
        if(nums[l] == target) return l;
        else return -1;
    }
    int upper_bound(vector<int> &nums,int target){
        int l = 0;
        int r = nums.size() - 1;
        while(l < r){
            int mid = (l + r + 1) / 2 ;
            if(nums[mid] == target) l = mid;
            else if(nums[mid] < target) l = mid + 1;
            else r = mid  - 1;
        }
        if(nums[r] == target) return l;
        else return -1;
    }
    vector<int> searchRange(vector<int>& nums, int target) {
        if(nums.size()==0) return {-1,-1};
        else return {lower_bound(nums,target),upper_bound(nums,target)};
    }
};

27.移除元素

题目链接：https://leetcode.cn/problems/remove-element/

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int cnt = nums.size();
        for(int i=0;i<cnt;i++){
            if(nums[i]==val){
                for(int j=i+1;j<cnt;j++) nums[j-1] = nums[j];
                cnt--;
                i--;
            }
        }
        return cnt;
    }
};