1996. The Number of Weak Characters in the Game

Description

You are playing a game that contains multiple characters, and each of the characters has two main properties: attack and defense. You are given a 2D integer array properties where properties[i] = [attacki, defensei] represents the properties of the ith character in the game.

A character is said to be weak if any other character has both attack and defense levels strictly greater than this character's attack and defense levels. More formally, a character i is said to be weak if there exists another character j where attackj > attacki and defensej > defensei.

Return the number of weak characters.

 

Example 1:

Input: properties = [[5,5],[6,3],[3,6]]
Output: 0
Explanation: No character has strictly greater attack and defense than the other.

Example 2:

Input: properties = [[2,2],[3,3]]
Output: 1
Explanation: The first character is weak because the second character has a strictly greater attack and defense.

Example 3:

Input: properties = [[1,5],[10,4],[4,3]]
Output: 1
Explanation: The third character is weak because the second character has a strictly greater attack and defense.

 

Constraints:

• 2 <= properties.length <= 105
• properties[i].length == 2
• 1 <= attacki, defensei <= 105

 

Solutions

Solution: Monotonic Stack

• Time complexity: O(nlogn)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {number[][]} properties
 * @return {number}
 */
const numberOfWeakCharacters = function (properties) {
  let maxDefense = 0;
  let result = 0;

  properties.sort((a, b) => b[0] - a[0] || a[1] - b[1]);

  for (const property of properties) {
    const defense = property[1];

    if (defense < maxDefense) result += 1;
    maxDefense = Math.max(defense, maxDefense);
  }
  return result;
};