[M差分] lc1109. 航班预订统计(差分+水题)

Posted 2021-09-16 Ypuyu

文章目录

• • 1. 题目来源
  • 2. 题目解析

1. 题目来源

链接：1109. 航班预订统计

2. 题目解析

差分即可，没啥意思。可以特判第 n 位的情况，省去数组 res 的空间开销。元素从 1 开始，-1 映射到从 0 开始即可。

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• 时间复杂度：$O(n)$。
• 空间复杂度：$O(n)$

---

class Solution {
public:
    vector<int> corpFlightBookings(vector<vector<int>>& bookings, int n) {
        vector<int> f(n + 1);
        for (auto book : bookings) f[book[0] - 1] += book[2], f[book[1]] -= book[2];
        for (int i = 1; i <= n; i ++ ) f[i] += f[i - 1];

        vector<int> res(n);
        for (int i = 0; i < n; i ++ ) res[i] = f[i];

        return res; 
    }
};

---

特判

class Solution {
public:
    vector<int> corpFlightBookings(vector<vector<int>>& bookings, int n) {
        vector<int> f(n);
        for (auto book : bookings) {
            int l = book[0], r = book[1] + 1, w = book[2];
            f[l - 1] += w;
            if (r - 1 < n) f[r - 1] -= w;
        }
        for (int i = 1; i < n; i ++ ) f[i] += f[i - 1];

        return f; 
    }
};