基础

Classical Binary Search [easy]

int findPosition(vector<int> &nums, int target) {
    int l=0, r=nums.size();
    while(l<r){
        int mid = l+(r-l)/2;
        if(nums[mid]==target) return mid;
        else if(target>nums[mid]) l= mid+1;
        else r=mid;
    }
    return -1;
}

First Position of Target [easy] (lower_bound)

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

Last Position of Target [easy] (upper_bound)

int lastPosition(vector<int> &nums, int target) {
    if(nums.empty()) return -1;
    int l=0, r=nums.size();
    while(l<r){
        int mid = l+(r-l)/2;
        if(nums[mid]<=target) l=mid+1;
        else r=mid;
    }
    return nums[r-1]==target ? r-1:-1;
}