什么是矩阵类二维数组中的 y * width + x

Question

我对这个陈述是如何工作的有点困惑this.content[y * width + x] = element(x, y));

class Matrix { 
constructor(width, height, element = (x, y) => undefined) { this.width = width; this.height = height; this.content = [];
//console.log(this.content);
for (let y = 0; y < height; y++) { 
for (let x = 0; x < width; x++) {
this.content[y * width + x] = element(x, y); 
console.log(this.content[y * width + x] = element(x, y));
} 
} 
} 
get(x, y) { return this.content[y * this.width + x]; } set(x, y, value) { this.content[y * this.width + x] = value; } }

class MatrixIterator { constructor(matrix) { this.x = 0; this.y = 0; this.matrix = matrix; } next() { if (this.y == this.matrix.height) return {done: true}; let value = {x: this.x, y: this.y, value: this.matrix.get(this.x, this.y)};
this.x++; if (this.x == this.matrix.width) { this.x = 0; this.y++; } return {value, done: false}; } }
Matrix.prototype[Symbol.iterator] = function() { return new MatrixIterator(this); };

//We can now loop over a matrix with for/of. 
let matrix = new Matrix(2, 2, (x, y) => `value ${x},${y}`);
console.log(matrix);
for (let {x, y, value} of matrix) { console.log(x, y, value);
}

// → 0 0 value 0,0 
// → 1 0 value 1,0 
// → 0 1 value 0,1 
// → 1 1 value 1,1

Answer 1

要识别矩阵的每个元素，显然需要使用索引，在这里本书的作者你在哪里找到这个，选择了这种方法来做到这一点：

y * this.width + x

这允许您访问矩阵的确定元素，同时识别所有元素，并保证不会与 .

重叠或者，您可以使用：[y + '_' + x]这样做与y * this.width + x的目的完全相同， 但是转换为字符串和串联使用循环来完成只需 2 个操作即可完成的事情！y * this.width和result + x. 这是用我的索引方式重写您的代码：

class Matrix {
constructor(width, height, element = (x, y) => undefined) {
this.width = width;
this.height = height;
this.content = {};//you need this for string keys !
//console.log(this.content);
for (let y = 0; y < height; y++) {
for (let x = 0; x < width; x++) {
this.content[y +'_'+ x] = element(x, y);
console.log((this.content[y +'_'+ x] = element(x, y)));
}
}
}
get(x, y) {
return this.content[y +'_'+ x];
}
set(x, y, value) {
this.content[y +'_'+ x] = value;
}
}
class MatrixIterator {
constructor(matrix) {
this.x = 0;
this.y = 0;
this.matrix = matrix;
}
next() {
if (this.y == this.matrix.height) return { done: true };
let value = {
x: this.x,
y: this.y,
value: this.matrix.get(this.x, this.y),
};
this.x++;
if (this.x == this.matrix.width) {
this.x = 0;
this.y++;
}
return { value, done: false };
}
}
//We can now loop over a matrix with for/of.
let matrix = new Matrix(2, 2, (x, y) => `value ${x},${y}`);
console.log('Matrix formed is : ',matrix);