Dijkstra 算法原理及js实现

时间  2019-12-05
标签 dijkstra 算法 原理 实现 栏目 JavaScript 繁體版
原文   原文链接

1. 用链表表示带权图

图片描述

  • 1.1 对链表头节点的描述
/** 节点 */
function V(data) {
    if (!(this instanceof V)) {
        return new V(data);
    }
    this._id = uuid(10, 10); //随机生成的 uuid
    this.data = data; //头节点的数据
    this.children = null; //指向链表的其它节点
    this.index = null; //节点在数组中的位置(数组下标)
    this.d = Infinity; //从源节点到当前节点的最短距离的估计指(初始位无穷大)
}
  • 1.2 对链表的其它节点的描述
function E() {
    if (!(this instanceof E)) {
        return new E();
    }
    this.next = null; //边指向下一个 E 类型的jie'dian
    this.index = null; // 边指向的节点在 Adj 中的下标 例如边 (u,v) 则 index 指向v
    this.w = null; //边的权重
}
  • 1.3 图
function G() {
    if (!(this instanceof G)) {
        return new G();
    }
    this.Adj = []; //构成图 G 的邻接链表
}

G.prototype = {
    constructor: G,
    // 添加边
    addEdge: function (u, v, w) {
        let e = E();
        e.index = v.index;
        e.w = w;
        let next = u.children;
        if (next == null) {
            u.children = e;
        } else {
            while (true) {
                if (next.next == null) {
                    next.next = e;
                    break;
                } else {
                    next = next.next;
                }
            }
        }
    },
    //获取节点 u 的全部邻接节点
    adj: function (u) {
        let next = u.children;
        let list = [];
        while (true) {
            if (next == null) {
                break;
            } else {
                list.push(this.Adj[next.index]);
                next = next.next;
            }
        }
        return list;
    },
    // 权重函数
    w: function (u, v) {
        let next = u.children;
        while (next != null) {
            if (this.Adj[next.index]._id == v._id) {
                return next.w;
            }
            next = next.next;
        }
    },
    // 添加节点
    addVertex: function (v) {
        if (v.index != null) {
            return;
        }
        let index = this.Adj.push(v) - 1; //该节点在数组中的位置
        v.index = index;
    },
    //松弛
    relax: function (u, v) {
        if (v.d > u.d + this.w(u, v)) {
            v.d = u.d + this.w(u, v);
            return true;
        }
        return false;
    }
}
  • 1.4 简单的 uuid
/** 生成一个简单的uuid len 表示长度, sys 表示进制 能够位 2, 8, 16 等等*/
function uuid(len, sys) {
    let chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');
    let uuid = [], i;
    sys = sys || chars.length;

    if (len) {
        for (i = 0; i < len; i++) uuid[i] = chars[0 | Math.random() * sys];
    } else {
        let r;
        uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';
        uuid[14] = '4';
        for (i = 0; i < 36; i++) {
            if (!uuid[i]) {
                r = 0 | Math.random() * 16;
                uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];
            }
        }
    }

    return uuid.join('');
}

2. Dijkstra 算法

Dijkstra 算法的思想是将图中的全部节点划分到两个集合中，集合Q中存放的是最短路径未肯定的节点，集合S中存放的是已经肯定最短路径距离的节点，初始时，全部的节点都在Q中，源节点s的最短路径距离初始时为0，集合Q内部经过最小优先队列来组织节点关系javascript

  1. 从最小优先队列Q中取出最短估计路径值最小的节点u
  2. 对u的全部邻接节点进行松弛操做，并更新Q中u的邻接节点的最短估计路径值
  3. 重复执行步骤1直至Q为空集
  • 2.1 松弛操做

松弛操做是对于节点 v，若是从源节点到v的最短估计路径距离为 v.d，v.d为无穷大或为某一具体数，u也是从源节点可达的节点，而且边(u, v)存在且距离是w，若是
v.d > u.d + w(u, v), 则 v.d = u.d + w(u, v)java

  • 2.2 最小优先队列

最小优先队列参照 二叉堆、堆排序、优先队列、topK问题详解及js实现 这里直接给出实现代码算法

function MinBinaryHeap(key) {
    if (!(this instanceof MinBinaryHeap))
        return new MinBinaryHeap(key);
    this.key = key; //key表示用来排序的字段
    this.size = 0; //堆大小 这里堆大小和数组大小一致
    this.list = []; //用于存放堆元素 存放的是对象
}
MinBinaryHeap.prototype = {
    constructor: MinBinaryHeap,
    //获取某个节点的父节点
    parent: function (i) {
        let p = Math.floor((i - 1) / 2);
        if (i > this.size - 1 || p < 0) return null;
        return p; //这里返回的 p 是在数组中的下标，数组是从0开始的
    },
    //获取某个节点的左孩子
    left: function (i) {
        let l = 2 * i + 1;
        if (l > this.size - 1) return null;
        return l;
    },
    //获取某个节点的右孩子
    right: function (i) {
        let r = 2 * i + 2;
        if (r > this.size - 1) return null;
        return r;
    },
    minHeapify: function (i) {
        let list = this.list;
        let key = this.key;
        let l = this.left(i);
        let r = this.right(i);
        let smallest = null;
        if (l != null) { //左孩子为空则右孩子必定为空
            if (r == null) smallest = l;
            else smallest = list[l][key] < list[r][key] ? l : r;
            if (list[i][key] <= list[smallest][key]) return;
            else {
                let t = list[i];
                list[i] = list[smallest];
                list[smallest] = t;
                this.minHeapify(smallest);
            }
        }
    },
    //元素上浮 对下标为i的元素进行向上调整，使堆保持其性质
    increase: function (i) {
        let list = this.list;
        let p = this.parent(i);
        while (i > 0 && list[p][this.key] > list[i][this.key]) { //i > 0 必定能保证 p != null
            let t = list[i];
            list[i] = list[p];
            list[p] = t;
            i = this.parent(i);
            p = this.parent(i);
        }
    },
    //构建堆
    buildHeap: function (a) {
        this.list = a;
        this.size = a.length;
        for (let i = Math.floor(a.length / 2) - 1; i > -1; i--) {
            this.minHeapify(i);
        }
    },
    //堆排序 由大到小
    heapSort: function (a) {
        this.buildHeap(a);
        for (let i = this.size - 1; i > 0; i--) {
            let t = this.list[0];
            this.list[0] = this.list[i];
            this.list[i] = t;
            this.size--;
            this.minHeapify(0);
        }
        return this.list;
    },
    //更新排序
    fresh: function() {
        this.size = this.list.length;
        for (let i = Math.floor(this.size / 2) - 1; i > -1; i--) {
            this.minHeapify(i);
        }
    }
}

//最小优先队列
function MinPriorityQueue(key, a) {
    if (!(this instanceof MinPriorityQueue)) {
        return new MinPriorityQueue(key, a);
    }
    if (a == null) {
        a = [];
    }
    this.minBinaryHeap = MinBinaryHeap(key);
    this.minBinaryHeap.buildHeap(a);
    this.key = key;
}
MinPriorityQueue.prototype = {
    constructor: MinPriorityQueue,
    insert: function (x) { //加入一个元素
        this.minBinaryHeap.size++;
        this.minBinaryHeap.list[this.minBinaryHeap.size - 1] = x;
        //向上调整
        this.minBinaryHeap.increase(this.minBinaryHeap.size - 1);
    },
    //remove 表示获取后是否删除 true 删除 false 不删除
    min: function (remove) { //获取最小元素
        let min = this.minBinaryHeap.list[0];
        if (remove) this.removeMin();
        return min;
    },
    removeMin: function () { //移除最小元素
        let list = this.minBinaryHeap.list;
        let size = this.minBinaryHeap.size;
        let min = list[0];
        list[0] = list[size - 1];
        list.shift(size - 1); //删除
        this.minBinaryHeap.size--;
        this.minBinaryHeap.minHeapify(0);
        return min;
    },
    update: function (i, x) { //更新元素
        this.minBinaryHeap.list[i] = x;
        this.minBinaryHeap.minHeapify(i);
        this.minBinaryHeap.increase(i);
    },
    fresh: function() {
        this.minBinaryHeap.fresh();
    }
}
  • 2.3 Dijkstra算法
function dijkstra(g, s) {
    let minPriorityQueue = MinPriorityQueue('d', null);
    s.d = 0; //初始s的最短路径距离
    g.Adj.forEach(v => {
        minPriorityQueue.insert(v);
    });
    let u = minPriorityQueue.removeMin(); //取出 d 值最小的节点
    while (u != null) {
        let adj = g.adj(u); //获取节点u的全部邻接节点
        adj.forEach(v => { //对u的全部邻接节点进行松弛操做
            let isRelax = g.relax(u, v);
            if(isRelax) {
                minPriorityQueue.fresh(); //刷新最小优先队列
            }
        });
        u = minPriorityQueue.removeMin();
    }
}

3. 测试及总体实现

图片描述

  • 3.1 测试代码
let g = G();
let v1 = V('v1');
let v2 = V('v2');
let v3 = V('v3');
let v4 = V('v4');
let v5 = V('v5');
g.addVertex(v1);
g.addVertex(v2);
g.addVertex(v3);
g.addVertex(v4);
g.addVertex(v5);
g.addEdge(v1, v2, 10);
g.addEdge(v1, v3, 5);
g.addEdge(v2, v4, 1);
g.addEdge(v2, v3, 2);
g.addEdge(v3, v4, 9);
g.addEdge(v3, v5, 2);
g.addEdge(v3, v2, 3);
g.addEdge(v4, v5, 4);
g.addEdge(v5, v4, 6);
g.addEdge(v5, v1, 7);

let a = dijkstra(g, v1);
console.log(g);
  • 3.2 总体代码及实现
function G() {
    if (!(this instanceof G)) {
        return new G();
    }
    this.Adj = [];
}

G.prototype = {
    constructor: G,
    // 添加边
    addEdge: function (u, v, w) {
        let e = E();
        e.index = v.index;
        e.w = w;
        let next = u.children;
        if (next == null) {
            u.children = e;
        } else {
            while (true) {
                if (next.next == null) {
                    next.next = e;
                    break;
                } else {
                    next = next.next;
                }
            }
        }
    },
    adj: function (u) {
        let next = u.children;
        let list = [];
        while (true) {
            if (next == null) {
                break;
            } else {
                list.push(this.Adj[next.index]);
                next = next.next;
            }
        }
        return list;
    },
    // 权重函数
    w: function (u, v) {
        let next = u.children;
        while (next != null) {
            if (this.Adj[next.index]._id == v._id) {
                return next.w;
            }
            next = next.next;
        }
    },
    // 添加节点
    addVertex: function (v) {
        if (v.index != null) {
            return;
        }
        let index = this.Adj.push(v) - 1; //该节点在数组中的位置
        v.index = index;
    },
    //松弛
    relax: function (u, v) {
        if (v.d > u.d + this.w(u, v)) {
            v.d = u.d + this.w(u, v);
            return true;
        }
        return false;
    }
}

/** 节点 */
function V(data) {
    if (!(this instanceof V)) {
        return new V(data);
    }
    this._id = uuid(10, 10);
    this.data = data;
    this.children = null;
    this.index = null; //节点在数组中的位置
    this.d = Infinity;
}

/** 边 */
function E() {
    if (!(this instanceof E)) {
        return new E();
    }
    this.next = null;
    this.index = null; // 边指向的节点 在Adj中的下标 例如边(u,v) 则 index 指向v
    this.w = null;
}

/** 生成一个简单的uuid */
function uuid(len, sys) {
    let chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');
    let uuid = [], i;
    sys = sys || chars.length;

    if (len) {
        for (i = 0; i < len; i++) uuid[i] = chars[0 | Math.random() * sys];
    } else {
        let r;
        uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';
        uuid[14] = '4';
        for (i = 0; i < 36; i++) {
            if (!uuid[i]) {
                r = 0 | Math.random() * 16;
                uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];
            }
        }
    }

    return uuid.join('');
}

function MinBinaryHeap(key) {
    if (!(this instanceof MinBinaryHeap))
        return new MinBinaryHeap(key);
    this.key = key; //key表示用来排序的字段
    this.size = 0; //堆大小 这里堆大小和数组大小一致
    this.list = []; //用于存放堆元素 存放的是对象
}
MinBinaryHeap.prototype = {
    constructor: MinBinaryHeap,
    //获取某个节点的父节点
    parent: function (i) {
        let p = Math.floor((i - 1) / 2);
        if (i > this.size - 1 || p < 0) return null;
        return p; //这里返回的 p 是在数组中的下标，数组是从0开始的
    },
    //获取某个节点的左孩子
    left: function (i) {
        let l = 2 * i + 1;
        if (l > this.size - 1) return null;
        return l;
    },
    //获取某个节点的右孩子
    right: function (i) {
        let r = 2 * i + 2;
        if (r > this.size - 1) return null;
        return r;
    },
    minHeapify: function (i) {
        let list = this.list;
        let key = this.key;
        let l = this.left(i);
        let r = this.right(i);
        let smallest = null;
        if (l != null) { //左孩子为空则右孩子必定为空
            if (r == null) smallest = l;
            else smallest = list[l][key] < list[r][key] ? l : r;
            if (list[i][key] <= list[smallest][key]) return;
            else {
                let t = list[i];
                list[i] = list[smallest];
                list[smallest] = t;
                this.minHeapify(smallest);
            }
        }
    },
    //元素上浮 对下标为i的元素进行向上调整，使堆保持其性质
    increase: function (i) {
        let list = this.list;
        let p = this.parent(i);
        while (i > 0 && list[p][this.key] > list[i][this.key]) { //i > 0 必定能保证 p != null
            let t = list[i];
            list[i] = list[p];
            list[p] = t;
            i = this.parent(i);
            p = this.parent(i);
        }
    },
    //构建堆
    buildHeap: function (a) {
        this.list = a;
        this.size = a.length;
        for (let i = Math.floor(a.length / 2) - 1; i > -1; i--) {
            this.minHeapify(i);
        }
    },
    //堆排序 由大到小
    heapSort: function (a) {
        this.buildHeap(a);
        for (let i = this.size - 1; i > 0; i--) {
            let t = this.list[0];
            this.list[0] = this.list[i];
            this.list[i] = t;
            this.size--;
            this.minHeapify(0);
        }
        return this.list;
    },
    //更新排序
    fresh: function() {
        this.size = this.list.length;
        for (let i = Math.floor(this.size / 2) - 1; i > -1; i--) {
            this.minHeapify(i);
        }
    }
}

//最小优先队列
function MinPriorityQueue(key, a) {
    if (!(this instanceof MinPriorityQueue)) {
        return new MinPriorityQueue(key, a);
    }
    if (a == null) {
        a = [];
    }
    this.minBinaryHeap = MinBinaryHeap(key);
    this.minBinaryHeap.buildHeap(a);
    this.key = key;
}
MinPriorityQueue.prototype = {
    constructor: MinPriorityQueue,
    insert: function (x) { //加入一个元素
        this.minBinaryHeap.size++;
        this.minBinaryHeap.list[this.minBinaryHeap.size - 1] = x;
        //向上调整
        this.minBinaryHeap.increase(this.minBinaryHeap.size - 1);
    },
    //remove 表示获取后是否删除 true 删除 false 不删除
    min: function (remove) { //获取最小元素
        let min = this.minBinaryHeap.list[0];
        if (remove) this.removeMin();
        return min;
    },
    removeMin: function () { //移除最小元素
        let list = this.minBinaryHeap.list;
        let size = this.minBinaryHeap.size;
        let min = list[0];
        list[0] = list[size - 1];
        list.shift(size - 1); //删除
        this.minBinaryHeap.size--;
        this.minBinaryHeap.minHeapify(0);
        return min;
    },
    update: function (i, x) { //更新元素
        this.minBinaryHeap.list[i] = x;
        this.minBinaryHeap.minHeapify(i);
        this.minBinaryHeap.increase(i);
    },
    fresh: function() {
        this.minBinaryHeap.fresh();
    }
}

function dijkstra(g, s) {
    let minPriorityQueue = MinPriorityQueue('d', null);
    s.d = 0;
    g.Adj.forEach(v => {
        minPriorityQueue.insert(v);
    });
    let u = minPriorityQueue.removeMin();
    while (u != null) {
        let adj = g.adj(u);
        adj.forEach(v => {
            let isRelax = g.relax(u, v);
            if(isRelax) {
                minPriorityQueue.fresh();
            }
        });
        u = minPriorityQueue.removeMin();
    }
}

let g = G();
let v1 = V('v1');
let v2 = V('v2');
let v3 = V('v3');
let v4 = V('v4');
let v5 = V('v5');
g.addVertex(v1);
g.addVertex(v2);
g.addVertex(v3);
g.addVertex(v4);
g.addVertex(v5);
g.addEdge(v1, v2, 10);
g.addEdge(v1, v3, 5);
g.addEdge(v2, v4, 1);
g.addEdge(v2, v3, 2);
g.addEdge(v3, v4, 9);
g.addEdge(v3, v5, 2);
g.addEdge(v3, v2, 3);
g.addEdge(v4, v5, 4);
g.addEdge(v5, v4, 6);
g.addEdge(v5, v1, 7);

let a = dijkstra(g, v1);
console.log(g);
  • 3.3 运行结果

将以上代码复制粘贴到浏览器控制台运行后结果为
图片描述segmentfault

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