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881.Boats-to-Save-People

881. Boats to Save People

题目地址

题目描述

The i-th person has weight people[i], and each boat can carry a maximum weight of limit.
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Each boat carries at most 2 people at the same time, provided the sum of the weight of those people is at most limit.
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Return the minimum number of boats to carry every given person. (It is guaranteed each person can be carried by a boat.)
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Example 1:
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Input: people = [1,2], limit = 3
Output: 1
Explanation: 1 boat (1, 2)
Example 2:
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Input: people = [3,2,2,1], limit = 3
Output: 3
Explanation: 3 boats (1, 2), (2) and (3)
Example 3:
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Input: people = [3,5,3,4], limit = 5
Output: 4
Explanation: 4 boats (3), (3), (4), (5)

代码

Approach 1: Greedy (two pointer)

Complexity Analysis
  • Time Complexity: O(NlogN), where N is the length of people.
  • Space Complexity: O(N).
class Solution {
public int numRescueBoats(int[] people, int limit) {
Arrays.sort(people); // O(nlogn)
int i = 0, j = people.length - 1;
int ans = 0;
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while (i <= j) {
ans++;
if (people[i] + people[j] <= limit) {
i++;
}
j--;
}
​
return ans;
}
}