LeetCode 1167. Minimum Cost to Connect Sticks

原題鏈接在這里：https://leetcode.com/problems/minimum-cost-to-connect-sticks/

題目：

You have some sticks with positive integer lengths.

You can connect any two sticks of lengths X and Y into one stick by paying a cost of X + Y.  You perform this action until there is one stick remaining.

Return the minimum cost of connecting all the given sticks into one stick in this way.

Example 1:

Input: sticks = [2,4,3]
Output: 14

Example 2:

Input: sticks = [1,8,3,5]
Output: 30

Constraints:

• 1 <= sticks.length <= 10^4
• 1 <= sticks[i] <= 10^4

題解：

Find the routine that add the two smallest first, then largest repeated the least times.

Use min heap to get two 2 smallest values, merge them and add merged back to min heap unitl there is only one stick in min heap.

Time Complexity: O(nlogn). n = sticks.length.

Space: O(n).

AC Java:

class Solution {
    public int connectSticks(int[] sticks) {
        if(sticks == null || sticks.length < 2){
            return 0;
        }
        
        PriorityQueue<Integer> minHeap = new PriorityQueue<>();
        for(int num : sticks){
            minHeap.add(num);
        }
        
        int res = 0;
        while(minHeap.size() > 1){
            int merge = minHeap.poll() + minHeap.poll();
            res += merge;
            minHeap.add(merge);
        }
        
        return res;
    }
}