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g1901_2000.s1921_eliminate_maximum_number_of_monsters.Solution Maven / Gradle / Ivy

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package g1901_2000.s1921_eliminate_maximum_number_of_monsters;

// #Medium #Array #Sorting #Greedy #2022_05_14_Time_19_ms_(90.78%)_Space_51.1_MB_(97.09%)

import java.util.Arrays;

/**
 * 1921 - Eliminate Maximum Number of Monsters\.
 *
 * Medium
 *
 * You are playing a video game where you are defending your city from a group of `n` monsters. You are given a **0-indexed** integer array `dist` of size `n`, where `dist[i]` is the **initial distance** in kilometers of the ith monster from the city.
 *
 * The monsters walk toward the city at a **constant** speed. The speed of each monster is given to you in an integer array `speed` of size `n`, where `speed[i]` is the speed of the ith monster in kilometers per minute.
 *
 * You have a weapon that, once fully charged, can eliminate a **single** monster. However, the weapon takes **one minute** to charge.The weapon is fully charged at the very start.
 *
 * You lose when any monster reaches your city. If a monster reaches the city at the exact moment the weapon is fully charged, it counts as a **loss** , and the game ends before you can use your weapon.
 *
 * Return _the **maximum** number of monsters that you can eliminate before you lose, or_ `n` _if you can eliminate all the monsters before they reach the city._
 *
 * **Example 1:**
 *
 * **Input:** dist = [1,3,4], speed = [1,1,1]
 *
 * **Output:** 3
 *
 * **Explanation:** 
 *
 * In the beginning, the distances of the monsters are [1,3,4]. You eliminate the first monster. 
 *
 * After a minute, the distances of the monsters are [X,2,3]. You eliminate the second monster. 
 *
 * After a minute, the distances of the monsters are [X,X,2]. You eliminate the thrid monster.
 *
 * All 3 monsters can be eliminated.
 *
 * **Example 2:**
 *
 * **Input:** dist = [1,1,2,3], speed = [1,1,1,1]
 *
 * **Output:** 1
 *
 * **Explanation:** 
 *
 * In the beginning, the distances of the monsters are [1,1,2,3]. You eliminate the first monster. 
 *
 * After a minute, the distances of the monsters are [X,0,1,2], so you lose. You can only eliminate 1 monster.
 *
 * **Example 3:**
 *
 * **Input:** dist = [3,2,4], speed = [5,3,2]
 *
 * **Output:** 1
 *
 * **Explanation:** 
 *
 * In the beginning, the distances of the monsters are [3,2,4]. You eliminate the first monster. 
 *
 * After a minute, the distances of the monsters are [X,0,2], so you lose. You can only eliminate 1 monster.
 *
 * **Constraints:**
 *
 * *   `n == dist.length == speed.length`
 * *   1 <= n <= 105
 * *   1 <= dist[i], speed[i] <= 105
**/
public class Solution {
    public int eliminateMaximum(int[] dist, int[] speed) {
        for (int i = 0; i < dist.length; i++) {
            dist[i] = (dist[i] - 1) / speed[i] + 1;
        }
        Arrays.sort(dist);
        int ans = 1;
        int time = 1;
        for (int i = 1; i < dist.length; i++) {
            if (dist[i] > time) {
                ans++;
                time++;
            } else {
                return ans;
            }
        }
        return ans;
    }
}




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