算法
相交链表
编写一个程序，找到两个单链表相交的起始节点。
输入：intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA = 2, skipB = 3
输出：Reference of the node with value = 8
输入解释：相交节点的值为 8 （注意，如果两个列表相交则不能为 0）。从各自的表头开始算起，链表 A 为 [4,1,8,4,5]，链表 B 为 [5,0,1,8,4,5]。在 A 中，相交节点前有 2 个节点；在 B 中，相交节点前有 3 个节点。
var getIntersectionNode = function(headA, headB) {
if(!headA || !headB) return null;
var countA = getListCount(headA);
var countB = getListCount(headB);
if (countA > countB) {
for (let i = countB; i < countA; i++) headA = headA.next;
} else if (countA < countB) {
for (let i = countA; i < countB; i++) headB = headB.next;
}
while(headA && headB){
if(headA === headB) return headA;
headA = headA.next;
headB = headB.next;
}
return null;
};
function getListCount(head){
var clone = head;
var count = 0;
while(clone){
++count;
clone = clone.next;
}
return count;
}
最佳实践：
let getIntersectionNode = function(headA, headB) {
if (!headA || !headB) return null;
let nodeA = headA;
let nodeB = headB;
while (nodeA !== nodeB) {
nodeA = nodeA === null ? headB : nodeA.next;
nodeB = nodeB === null ? headA : nodeB.next;
}
return nodeA;
}
绘制立体图形
一个立方体由六个面组成，每个面是由2个三角组成，总共应该是由12个三角形组成，12个三角形又是由 8 个顶点组成，所以如果要完全由三角形去拼接的话，顶点的缓冲区就会很大，并且很多都是重复的点，所以绘制立方体时先将所有的点和颜色先存储在一个缓冲区，再用另一个数组存储索引的缓冲区，用索引构建所有的面，将一个顶点描述的数组，改成了一个数组+索引描述的两个数组，缓冲区复杂度会减小，可读性增加。
initVertexBuffers(gl){
var verticesColors = new Float32Array([
// Vertex coordinates and color
1.0, 1.0, 1.0, 1.0, 1.0, 1.0, // v0 White
-1.0, 1.0, 1.0, 1.0, 0.0, 1.0, // v1 Magenta
-1.0, -1.0, 1.0, 1.0, 0.0, 0.0, // v2 Red
1.0, -1.0, 1.0, 1.0, 1.0, 0.0, // v3 Yellow
1.0, -1.0, -1.0, 0.0, 1.0, 0.0, // v4 Green
1.0, 1.0, -1.0, 0.0, 1.0, 1.0, // v5 Cyan
-1.0, 1.0, -1.0, 0.0, 0.0, 1.0, // v6 Blue
-1.0, -1.0, -1.0, 0.0, 0.0, 0.0 // v7 Black
]);
// 顶点索引
var indices = new Uint8Array([ //(Uint8Array)是无符号8位整型数
0, 1, 2, 0, 2, 3, // front
0, 3, 4, 0, 4, 5, // right
0, 5, 6, 0, 6, 1, // up
1, 6, 7, 1, 7, 2, // left
7, 4, 3, 7, 3, 2, // down
4, 7, 6, 4, 6, 5 // back
]);
// Create a buffer object
var vertexColorBuffer = gl.createBuffer();
var indexBuffer = gl.createBuffer();
if (!vertexColorBuffer || !indexBuffer) {
return -1;
}
// Write the vertex coordinates and color to the buffer object
gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);
var FSIZE = verticesColors.BYTES_PER_ELEMENT;
// Assign the buffer object to a_Position and enable the assignment
var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
if(a_Position < 0) {
console.log('Failed to get the storage location of a_Position');
return -1;
}
gl.vertexAttribPointer(a_Position, 3, gl.FLOAT, false, FSIZE * 6, 0);
gl.enableVertexAttribArray(a_Position);
// Assign the buffer object to a_Color and enable the assignment
var a_Color = gl.getAttribLocation(gl.program, 'a_Color');
if(a_Color < 0) {
console.log('Failed to get the storage location of a_Color');
return -1;
}
gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 6, FSIZE * 3);
gl.enableVertexAttribArray(a_Color);
// 将顶点索引数据写入缓冲区对象
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
return indices.length;
}
var VSHADER_SOURCE = `
attribute vec4 a_Position;
attribute vec4 a_Color;
uniform mat4 u_MvpMatrix;
varying vec4 v_Color;
void main() {
gl_Position = u_MvpMatrix * a_Position;
gl_PointSize = 10.0;
v_Color = a_Color;
}
`;
var FSHADER_SOURCE = `
precision mediump float;
varying vec4 v_Color;
void main() {
gl_FragColor = v_Color;
}
`;
var gl = canvas.getContext('webgl');
initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)
this.gl = gl;
var n = this.initVertexBuffers(gl)
//设置视点、视线、上方向
var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix');
var mvpMatrix = new Matrix4();
mvpMatrix.setPerspective(30, 1, 1 ,100);
mvpMatrix.lookAt(3, 3, 7, 0, 0, 0, 0, 1, 0);
gl.uniformMatrix4fv(u_MvpMatrix, false, mvpMatrix.elements);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);