letcode 分类练习 二分查找 双指针

二分查找

区间的方式去看待，防止边界错误
左闭右闭的思想
$$[x,y]\to [\text{left},\text{right}]$$

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

双指针法

快慢双指针法解决

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

首尾双指针解决

class Solution {
public:
    vector<int> sortedSquares(vector<int>& nums) {
        int n = nums.size();
        vector<int> result(n, 0);
        int left = 0; int right = nums.size() - 1;
        int k = nums.size() - 1;
        while(left <= right){
            if(nums[left] * nums[left] >= nums[right] * nums[right]){
                result[k--] = nums[left] * nums[left];
                left ++;
            }else{
                result[k--] = nums[right] * nums[right];
                right --;
            }
        }
        return result;
    }
};