leetcode 查找

解法1：

直接使用STL：

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        const int l = distance(nums.begin(), lower_bound(nums.begin(), nums.end(), target));
        const int u = distance(nums.begin(), prev(upper_bound(nums.begin(), nums.end(), target)));
        if(nums[l] != target)
            return vector<int> {-1, -1};
        else
            return vector<int> {l, u};
    }
};

解法2：

二分查找，分别找到第一个和最后一个数

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

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

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        int m = matrix.size();
        int n = matrix.front().size();
        int first = 0, last = m * n - 1;
        while(first <= last){
            int mid = (first + last) / 2;
            if(matrix[mid / n][mid % n] == target)
                return true;
            else if(matrix[mid / n][mid % n] > target)
                last = mid - 1;
            else
                first = mid + 1;
        }
        return false;
    }
};