LeetCode34. 在排序数组中查找元素的第一个和最后一个位置

有序递增重复序列边界二分查找，详见二分总结博客；

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

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

vector searchRange(vector& nums, int target) {
    if(nums.size()<1)
        return vector{-1,-1};
    if(nums.size()==1)
        if(target==nums[0])
            return vector{0,0};
        else
            return vector{-1,-1};
    int l= left_bound(nums,target);
    int r= right_bound(nums,target);
    return vector{l,r};
}