Wood Cut

19% Accepted

Given n pieces of wood with length L[i] (integer array).
Cut them into small pieces to guarantee you could have equal or more than k pieces with the same length.
What is the longest length you can get from the n pieces of wood? Given L & k, return the maximum length of the small pieces.

Have you met this question in a real interview? Yes
Example
For L=[232, 124, 456], k=7, return 114.

Note

• You couldn't cut wood into float length.

Challenge

• O(n log Len), where Len is the longest length of the wood.

Tags Expand

• Binary Search

思路

• 仔细看题 nlog(len) n代表的是数组长度
• brute force的话，n*len
• 这样就要优化len, 通过二分去查找大概的区间
• 也就是二分查找 增加判断条件就可以了

public class Solution {
    /**
     *@param L: Given n pieces of wood with length L[i]
     *@param k: An integer
     *return: The maximum length of the small pieces.
     */
    public int woodCut(int[] L, int k) {
        int max = 0;
        for (int i = 0; i < L.length; i++) {
            max = Math.max(max, L[i]);
        }

        // find the largest length that can cut more than k pieces of wood.
        int start = 1, end = max;
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (count(L, mid) >= k) {
                start = mid;
            } else {
                end = mid;
            }
        }

        if (count(L, end) >= k) {
            return end;
        }
        if (count(L, start) >= k) {
            return start;
        }
        return 0;
    }

    private int count(int[] L, int length) {
        int sum = 0;
        for (int i = 0; i < L.length; i++) {
            sum += L[i] / length;
        }
        return sum;
    }
}