二分模板

using namespace std;
//二分模板
class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        vector<int> ans={-1,-1};
        int n = nums.size();
        if(n==0) return ans;
        //闭区间
        int l = 0;
        int r = n-1;
        //找最左边
        while(l <= r){
            int mid = l+(r-l)/2;
            if(nums[mid] < target) l = mid+1;
            else if( target < nums[mid]) r = mid-1;
            else r = mid-1;
        }
        if(!(l >= n || nums[l]!=target)) ans[0] = l;
        l = 0;
        r = n-1;
        
        //找右边
        while(l<=r){

            int mid = l+(r-l)/2;
            if(nums[mid] < target) l = mid+1;
            else if( target < nums[mid]) r = mid-1;
            else  l = mid+1;
        }
        if(!(r<0 || nums[r]!=target)) ans[1] = r;
        
        //找目标值
        l =0;
        r = n-1;
        int ret =-1;
        while(l<=r){
            int mid = l+(r-l)/2;
            if(nums[mid] < target) l = mid+1;
            else if( target < nums[mid]) r = mid-1;
            else {
                ret = mid;
                break;
            }
        }
    }
};