算法训练营 Day1 数组part01

一、 704. 二分查找

左闭右闭区间

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

二、27. 移除元素

暴力求解法

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int size = nums.size();
        for (int i = 0; i < size; i++) {
            if (nums[i] == val) { // 发现需要移除的元素，就将数组集体向前移动一位
                for (int j = i + 1; j < size; j++) {
                    nums[j - 1] = nums[j];
                }
                i--; // 因为下标i以后的数值都向前移动了一位，所以i也向前移动一位
                size--; // 此时数组的大小-1
            }
        }
        return size;

    }
};

双指针法

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

三、977.有序数组的平方

暴力求解

class Solution {
public:
    vector<int> sortedSquares(vector<int>& nums) {
        for (int i = 0; i < nums.size(); i++) {
            nums[i] *= nums[i];
        }
        sort(nums.begin(), nums.end());
        return nums;
    }
};

双指针法

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