3分钟做5道leetcode题上手leetcode刷题之路

2019/9/28 posted in leetcode

在官网注册后，点击题库页面就可以看到所有可以刷的题目了

可以按照难度进行筛选、建议从简单难度的题上手

两数之和: https://leetcode-cn.com/problems/two-sum/

问题描述

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> res;
        bool resolve = false;
        for (int i = 0; i < nums.size() - 1; i ++) {
            for (int j = i + 1; j < nums.size(); j ++){
                if (nums[i] + nums[j] == target) {
                    res.push_back(i);
                    res.push_back(j);
                    resolve = true;
                    break;
                }
            }
            if (resolve) {
                break;
            }
        }
        return res;
    }
};

然后提交就可以看到统计信息了

leetcode题的答案不止一种，可以根据cpu和内存使用的反馈进行调优。

2的幂: https://leetcode-cn.com/problems/power-of-two/

class Solution {
public:
    bool isPowerOfTwo(long n) {
        return n != 0 && (n & (n -1)) == 0;
    }
};

可以在题解界面查看其它同学的解题思路

4的幂: https://leetcode-cn.com/problems/power-of-four

class Solution {
public:
    bool isPowerOfFour(long n) {
        return n != 0 && (n & 0xAAAAAAAA) == 0 && (n & (n -1)) == 0;
    }
};

斐波拉契数: https://leetcode-cn.com/problems/fibonacci-number/

class Solution {
public:
    int fib(int n) {
        if (n == 0) {
            return 0;
        }
        if (n <= 2) {
            return 1;
        }
        int a = 1, b = 1, i = 3, res = 0;
        while (i <= n) {
            res = a + b;

            a = b;
            b = res;
            i ++;
        }
        return res;
    }
};

移除元素: https://leetcode-cn.com/problems/remove-element/

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int find = 0;
        
        int j = nums.size();
        for (int i = 0; i < j; i ++) {
            cout << "i: " << i << " num:" << nums[i] << endl;
            if (nums[i] == val) {
                find ++;
                swap(nums[i], nums[j - 1]);
                j --;
                i --;
            }
        }
        
        return nums.size() - find;
    }
};

回文数：https://leetcode-cn.com/problems/palindrome-number/

class Solution {
public:
    bool isPalindrome(int x) {
        int from = x;
        if (x < 0) {
            return false;
        }
        vector<int> numBits;
        while (from > 0) {
            numBits.insert(numBits.begin(), from % 10);
            from = from / 10;
        }
        
        int res = 0;
        for (int i = 0; i < numBits.size(); i ++) {
            res += numBits[i] * pow(10, i);
        }
        if (res == x) {
            return true;
        } else {
            return false;
        }
    }
};