Given n points on a 2D plane, find if there is such a line parallel to y-axis that reflect the given points.
Example 1:
Given points = [[1,1],[-1,1]]
, return true
.
Example 2:
Given points = [[1,1],[-1,-1]]
, return false
.
Follow up:
Could you do better than O(n2)?
思路:假设如果存在这样的一条对称轴,那么对于一对对称点,它们的X坐标之和应该是个定值。
我们找到所有点中X坐标的最小值和最大值,两者之和就是这个定值。
然后将所有点的坐标记录在set中,然后判断每个点的对称点是否在set中。
时间复杂度O(N)。
1 class Solution { 2 public: 3 bool isReflected(vector<pair<int, int>>& points) { 4 if (points.size() == 0) return true; 5 unordered_set<string> p; 6 int minX = INT_MAX, maxX = INT_MIN; 7 for (int i = 0; i < points.size(); i++) { 8 int x = points[i].first, y = points[i].second; 9 minX = std::min(minX, x); 10 maxX = std::max(maxX, x); 11 string code = std::to_string(x) + "|" + std::to_string(y); 12 p.insert(code); 13 } 14 int sum = minX + maxX; 15 for (int i = 0; i < points.size(); i++) { 16 int x = sum - points[i].first, y = points[i].second; 17 string code = std::to_string(x) + "|" + std::to_string(y); 18 if (p.count(code) == 0) return false; 19 } 20 return true; 21 } 22 };
时间: 2024-10-08 19:54:37