Link: https://leetcode.cn/problems/maximum-population-year/

Question

difficulty: easy
adj diff: 2

You are given a 2D integer array logs where each logs[i] = [birthi, deathi] indicates the birth and death years of the ith person.

The population of some year x is the number of people alive during that year. The ith person is counted in year x's population if x is in the inclusive range [birthi, deathi - 1]. Note that the person is not counted in the year that they die.

Return the earliest year with the maximum population.

Example 1:

Input: logs = [[1993,1999],[2000,2010]]
Output: 1993
Explanation: The maximum population is 1, and 1993 is the earliest year with this population.

Example 2:

Input: logs = [[1950,1961],[1960,1971],[1970,1981]]
Output: 1960
Explanation:
The maximum population is 2, and it had happened in years 1960 and 1970.
The earlier year between them is 1960.

Constraints:

	1 <= logs.length <= 100
	1950 <= birthi < deathi <= 2050

Code

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public int maximumPopulation(int[][] logs) {
    // an array of population increase/decrease from 1950 to 2050
    int[] increase = new int[101];
    for (int[] people: logs) {
        increase[people[0] - 1950]++;
        increase[people[1] - 1950]--;
    }

    // an array of total population from 1950 to 2050
    int[] population = new int[101];
    population[0] = increase[0];
    int maxYear = 0;
    for (int i = 1; i < 101; i++) {
        population[i] = population[i - 1] + increase[i];
        if (population[i] > population[maxYear]) {
            maxYear = i;
        }
    }
    return maxYear + 1950;
}