js杨辉三角

function Tree() {
            this.lines = [
                [1]
            ]
        }
        var pp = Tree.prototype
        pp.genNode = function(line, i) {
            var top = line - 1
            var topLine = this.lines[top] || [0, 0, 0]
            var curLine = this.lines[line]
            if (!curLine) {
                curLine = this.lines[line] = []
            }
            if (i in curLine)
                return
            curLine[i] = (topLine[i - 1] || 0) + (topLine[i] || 0)
        }
        pp.genLine = function(n) {
            for (var i = 0; i <= n; i++) {
                this.genNode(n, i)
            }
        }
        pp.print = function() {
            for (var i = 0; i < this.lines.length; i++) {
                var el = this.lines[i]
                console.log(el.join(', '))
            }
        }
        var tree = new Tree
        for (var i = 0; i < 10; i++) {
            tree.genLine(i)
        }

        tree.print()