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package class25;
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import java.util.HashMap;
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import java.util.Map;
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// 本题测试链接: https://leetcode.com/problems/max-points-on-a-line/
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public class Code03_MaxPointsOnALine {
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// [
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// [1,3]
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// [4,9]
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// [5,7]
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// ]
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public static int maxPoints(int[][] points) {
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if (points == null) {
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return 0;
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}
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if (points.length <= 2) {
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return points.length;
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}
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// key = 3
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// value = {7 , 10} -> 斜率为3/7的点 有10个
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// {5, 15} -> 斜率为3/5的点 有15个
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Map<Integer, Map<Integer, Integer>> map = new HashMap<Integer, Map<Integer, Integer>>();
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int result = 0;
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for (int i = 0; i < points.length; i++) {
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map.clear();
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int samePosition = 1;
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int sameX = 0;
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int sameY = 0;
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int line = 0;
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for (int j = i + 1; j < points.length; j++) { // i号点，和j号点，的斜率关系
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int x = points[j][0] - points[i][0];
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int y = points[j][1] - points[i][1];
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if (x == 0 && y == 0) {
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samePosition++;
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} else if (x == 0) {
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sameX++;
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} else if (y == 0) {
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sameY++;
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} else { // 普通斜率
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int gcd = gcd(x, y);
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x /= gcd;
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y /= gcd;
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// x / y
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if (!map.containsKey(x)) {
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map.put(x, new HashMap<Integer, Integer>());
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}
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if (!map.get(x).containsKey(y)) {
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map.get(x).put(y, 0);
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}
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map.get(x).put(y, map.get(x).get(y) + 1);
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line = Math.max(line, map.get(x).get(y));
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}
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}
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result = Math.max(result, Math.max(Math.max(sameX, sameY), line) + samePosition);
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}
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return result;
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}
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// 保证初始调用的时候，a和b不等于0
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// O(1)
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public static int gcd(int a, int b) {
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return b == 0 ? a : gcd(b, a % b);
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}
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}
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