标签:crosses 335 Self metres && Crossing Input line true
You are given an array x of
n
positive numbers. You start at point(0,0)
and movesx[0]
metres to the north, thenx[1]
metres to the west,x[2]
metres to the south,x[3]
metres to the east and so on. In other words, after each move your direction changes counter-clockwise.Write a one-pass algorithm with
O(1)
extra space to determine, if your path crosses itself, or not.
Example 1:
┌───┐ │ │ └───┼──> │ Input:[2,1,1,2]
Output: trueExample 2:
┌──────┐ │ │ │ │ └────────────> Input:[1,2,3,4]
Output: falseExample 3:
┌───┐ │ │ └───┼> Input:[1,1,1,1]
Output: true
Approach #1: Math. [Java]
class Solution { public boolean isSelfCrossing(int[] x) { if (x.length < 4) return false; for (int i = 3; i < x.length; ++i) { if (x[i] >= x[i-2] && x[i-3] >= x[i-1]) return true; if (i >= 4) { if (x[i-3] == x[i-1] && x[i] + x[i-4] >= x[i-2]) return true; } if (i >= 5) { if (x[i-2] >= x[i-4] && x[i-1] + x[i-5] >= x[i-3] && x[i] >= x[i-2] - x[i-4] && x[i-1] <= x[i-3]) return true; } } return false; } }
Analysis:
Categarize the self-crossing scenarios, there are 3 of them:
1. Fourth line crosses first line and works for fifth line crosses second 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.
Reference:
https://leetcode.com/problems/self-crossing/discuss/79131/Java-Oms-with-explanation
标签:crosses,335,Self,metres,&&,Crossing,Input,line,true 来源: https://www.cnblogs.com/ruruozhenhao/p/10809104.html
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