LeetCode1523. Count Odd Numbers in an Interval Range

一、题目

Given two non-negative integers low and high. Return the count of odd numbers between low and high (inclusive).

Example 1:

Input: low = 3, high = 7
Output: 3
Explanation: The odd numbers between 3 and 7 are [3,5,7].
Example 2:

Input: low = 8, high = 10
Output: 1
Explanation: The odd numbers between 8 and 10 are [9].

Constraints:

0 <= low <= high <= 10^9

二、题解

首先考虑两侧均是偶数的情况：奇数数量为(high - low) / 2
若左侧是奇数，则数量加一，并右移，使其变为偶数。
若右侧是奇数，则数量减一，并左移，使其变为偶数。
最终，如果左侧或右侧是奇数，可以转换为左右侧均为偶数的情况计算。

class Solution {
public:
    int countOdds(int low, int high) {
        int res = 0;
        if(low % 2 != 0){
            res++;
            low++;
        }
        if(high % 2 != 0){
            res++;
            high--;
        }
        res += (high - low) / 2;
        return res;
    }
};