差分数组算法

详情

1094. 拼车

java 复制代码

class Solution {
    public boolean carPooling(int[][] trips, int capacity) {
        TreeMap<Integer, Integer> diff = new TreeMap<>();
        for (int[] trip : trips) {
            int num = trip[0], from = trip[1], to = trip[2];
            diff.merge(from, num, Integer::sum);
            diff.merge(to, -num, Integer::sum);
        }
        int sum = 0;
        for (int v: diff.values()) {
            sum += v;
            if (sum > capacity) {
                return false;
            }
        }
        return true;
    }
}

1109. 航班预订统计

java 复制代码

class Solution {
    public int[] corpFlightBookings(int[][] bookings, int n) {
        int[] res = new int[n + 1]; // 离开在后一个离开
        for (int[] booking : bookings) {
            int first = booking[0], last = booking[1], seat = booking[2];
            res[first - 1] += seat;
            res[last] -= seat;
        }

        for (int i = 1; i < n; i++) {
            res[i] += res[i - 1];
        }
        int[] ans = new int[n];
        System.arraycopy(res, 0, ans, 0, n);
        return ans;
    }
}

121. 买卖股票的最佳时机

java 复制代码

class Solution {
    public int maxProfit(int[] prices) {
        int res = 0;
        int minPrice = prices[0];
        for (int price : prices) {
            res = Math.max(res, price - minPrice);  // 计算
            minPrice = Math.min(minPrice, price);   // 维护左边出现的最小价格
        }
        return res;
    }
}

122. 买卖股票的最佳时机 II

java 复制代码

class Solution {
    public int maxProfit(int[] prices) {
        int n = prices.length;
        int[] diff = new int[n];
        diff[0] = prices[0];
        int res = 0;
        for (int i = 1; i < n; i++) {
            diff[i] = prices[i] - prices[i - 1];
            res += Math.max(diff[i], 0);
        }
        return res;
    }
}

253. 会议室II

给定一个会议时间安排的数组，每个会议时间都会包括开始和结束的时间 $\[ s 1 , e 1$ , $s 2 , e 2$ , . . . ] ( s i < e i ) $\[s_1,e_1$ , $s_2,e_2$ ,...] (s_i < e_i) $\[s1,e1$ , $s2,e2$ ,...](si<ei)，为避免会议冲突，同时要考虑充分利用会议室资源，请你计算至少需要多少间会议室，才能满足这些会议安排。

复制代码

示例 1:
输入: [[0, 30],[5, 10],[15, 20]]
输出: 2

示例 2:
输入: [[7,10],[2,4]]
输出: 1

java 复制代码

public class Solution {
    int minMeetingRooms(int[][] intervals) {
        int n = 10001;
        int[] diff = new int[n];
        for (int[] interval : intervals) {
            int start = interval[0], end = interval[1];
            diff[start] += 1;
            diff[end] -= 1;
        }
        int res = 0;
        for (int i = 1; i < n; i++) {
            diff[i] = diff[i - 1] + diff[i];
            res = Math.max(res, diff[i]);
        }
        return res;
    }
}