在没有任何循环的情况下比较不同大小的数组 [英] Comparing arrays of different sizes without any loop

问题描述

问题是这样的:

给定两个数组，a &b(均为正整数).

Given two arrays, a & b (both with positive integers).

special number 是 a(i) == i 的数字(值等于索引).

A special number is a number which a(i) == i (the value equals to the index).

如何检查数组 b 是否包含 a 的 特殊数字 的值.

How can you check if array b contains a value which is a special number of a.

例如:a = [9 9 3 9]、b = [3 4 5].输出将是 3.如果 b 或 a 为空，则输出为 0.如果b包含多个特殊数字，只会显示最小的一个.

For example: a = [9 9 3 9], b = [3 4 5]. Output will be 3. If b or a are empty, output is 0. If b contains several special number, only the smallest one will be shown.

这是我到目前为止所做的事情，无法从这里取得进展..

This is what I have managed to do by far, can't progress from here..

a = input('Please enter the array a : ');
b = input('Please enter the array b : ');

indexedArray = 1:length(a);
c = a-indexedArray;
t = find(c==0);   
p = find(t==b);

不工作.

顺便说一句:只能使用这些功能:.排序、 isempty 、 all 、 any 、 find 、 sum 、 max 、 min 、 长度.没有循环或条件！只允许使用数组.没有矩阵.不能使用 &、|

谢谢！

推荐答案

我推迟发布我的解决方案，因为我 正确怀疑这个问题是家庭作业.但是，由于 OP 已接受 Jonas 的回答，我不妨发布我的.

I was holding off posting my solution because I correctly suspected that this question was a homework assignment. However, since the OP has accepted Jonas's answer, I might as well post mine.

sum、length、any 和 min 的组合可以解决问题:

A combination of sum, length, any, and min does the trick:

function out = stupidTutor(a, b)

a        = sum(a, 1);           % if a is empty, replace it by a 1-by-0 matrix
specials = a(a == 1:length(a)); % construct the vector of special numbers
b        = sum(b, 1);           % if b is empty, replace it by a 1-by-0 matrix

% some dyadic-product shenanigans
A   = specials' * (b == b);
B   = (specials == specials)' * b;
ind = any(A == B, 1);

temp = min(b(ind));         % temp is either a scalar, a 1-by-0 matrix, or []
out  = sum(sum(temp, 2), 1); % trick to return 0 in case temp be 1-by-0 or []

测试

%               a           b                 result
stupidTutor([9 9 3 9]  , [3 4 5])       %       3  
stupidTutor([9 9 3 9]  , [9 8])         %       0
stupidTutor([9 9 9 9 5], [3 4 5 3])     %       5
stupidTutor([9 9 3 9 5], [3 4 5 3])     %       3
stupidTutor([9 9 3 9 5], [5 4 3 2 1])   %       3
stupidTutor([9 9 3 9]  , [])            %       0
stupidTutor([]         , [3 4 5])       %       0
stupidTutor([]         , [])            %       0

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