[CSDN] 【Leetcode】396.RotateFunction

发表于:  阅读量:12369

摘要

题目链接:题目:Givenanarrayofintegers A andlet n tobeitslength.Assume Bk tobeanarrayo...

题目链接:

题目:

Given an array of integers A and let n to be its length.

Assume Bk to be an array obtained by rotating the array A k positions clock-wise, we define a "rotation function" F on A as follow:

F(k) = 0 * Bk[0] + 1 * Bk[1] + ... + (n-1) * Bk[n-1].

Calculate the maximum value of F(0), F(1), ..., F(n-1).

Note:
n is guaranteed to be less than 105.

Example:

A = [4, 3, 2, 6]

F(0) = (0 * 4) + (1 * 3) + (2 * 2) + (3 * 6) = 0 + 3 + 4 + 18 = 25
F(1) = (0 * 6) + (1 * 4) + (2 * 3) + (3 * 2) = 0 + 4 + 6 + 6 = 16
F(2) = (0 * 2) + (1 * 6) + (2 * 4) + (3 * 3) = 0 + 6 + 8 + 9 = 23
F(3) = (0 * 3) + (1 * 2) + (2 * 6) + (3 * 4) = 0 + 2 + 12 + 12 = 26

So the maximum value of F(0), F(1), F(2), F(3) is F(3) = 26.

思路:

啊 没想到这次contest中 我遇到最难的题是这道。。。用F(k)=F(k-1)-(n-1)*end+(sum-end)  + 0*end = F(k-1)+sum-n*end

画了个图:


算法:

	public int maxRotateFunction(int[] A) {
		int max=Integer.MIN_VALUE;
		int sum = 0;
		int pre = 0;
		
		for(int i=0;i<A.length;i++){
			pre +=A[i]*i;
			sum+=A[i];
		}
		max = Math.max(pre, max);

		int k=1;
		while(k<A.length){
			int res = pre+sum-A.length*A[A.length-k];
			max = Math.max(max, res);
			pre = res;
			k++;
		}
		
		return max;
	}





关键词: Leetcode题解java版
-->
渝ICP备16002246号 Copyright © 2017. Singee77.com