335. Self Crossing

最新推荐文章于 2024-08-28 07:25:21 发布

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最新推荐文章于 2024-08-28 07:25:21 发布

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原文链接：http://www.cnblogs.com/zmyvszk/p/5659041.html

本文介绍了一种用于判断二维平面上由一系列线段组成的路径是否出现交叉的算法。该算法通过三种不同的交叉场景来判断：第四条线段与第一条线段交叉；第五条线段与第一条线段相交；第六条线段与第一条线段交叉。

    /*
     * 335. Self Crossing
     * 2016-7-10 by Mingyang
     */
    // Categorize the self-crossing scenarios, there are 3 of them: 
    // 1. Fourth line crosses first line and works for fifth line crosses second line and so on...
    // 2. Fifth line meets first line and works for the lines after
    // 3. Sixth line crosses first line and works for the lines after
    public boolean isSelfCrossing(int[] x) {
        int l = x.length;
        if(l <= 3) return false;
        
        for(int i = 3; i < l; i++){
            if(x[i] >= x[i-2] && x[i-1] <= x[i-3]) return true;  //Fourth line crosses first line and onward
            if(i >=4)
            {
                if(x[i-1] == x[i-3] && x[i] + x[i-4] >= x[i-2]) return true; // Fifth line meets first line and onward
            }
            if(i >=5)
            {
                if(x[i-2] - x[i-4] >= 0 && x[i] >= x[i-2] - x[i-4] && x[i-1] >= x[i-3] - x[i-5] && x[i-1] <= x[i-3]) return true;  // Sixth line crosses first line and onward
            }
        }
        return false;
    }