704、二分查找

第一反应当然是调库啦~

class Solution {
public:
    int search(vector<int>& nums, int target) {
        int n = nums.size();
        auto it = lower_bound(nums.begin(), nums.end(), target);
        if (it == nums.end()) return -1;
        if (*it != target) return -1;
        return it - nums.begin();
    }
};

再手写下二分

class Solution {
public:
    int search(vector<int>& nums, int target) {
        int n = nums.size();
        int L = 0, R = n - 1;
        while (L < R)
        {
            int mid = (L + R) >> 1;
            if (nums[mid] == target) return mid;
            if (nums[mid] < target) L = mid + 1;
            else R = mid;
        }
        if (nums[L] == target) return L;
        return -1;
    }
};

27. 移除元素

前后双指针

// 双指针
class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int n = nums.size();
        int slow = 0, fast = 0;
        while (fast < n)
        {
            if (nums[fast] != val) nums[slow++] = nums[fast];
            fast ++;
        }
        return slow;
    }
};