[leetCode刷题笔记]2017.04.04

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67. Add Binary

真不知道String builder还有reverse方法。。。本来都准备用Stack了。。。

public class Solution {    public String addBinary(String a, String b) {               StringBuilder sb = new StringBuilder();        int i = a.length() - 1, j = b.length() - 1, promote = 0;        while (i >=0  || j >= 0) {            int sum = promote;            if (i >= 0) sum += a.charAt(i--) - '0';            if (j >= 0) sum += b.charAt(j--) - '0';            sb.append(sum % 2);            promote = sum / 2;        }        if (promote != 0) sb.append(promote);        return sb.reverse().toString();    }}

149. Max Points on a Line

这道题没有AC，因为double对这个test case：

[[0,0],[94911151,94911150],[94911152,94911151]]精度不够。

比较好的方法是产生最大公约数，再用x 和y一起作为key。

/** * Definition for a point. * class Point { *     int x; *     int y; *     Point() { x = 0; y = 0; } *     Point(int a, int b) { x = a; y = b; } * } */public class Solution {    public int maxPoints(Point[] points) {        if (points.length <= 1) {            return points.length;        }                        int max = 0;        for (int i = 0; i < points.length - 1; i++) {            int dup = 1;            Map<Double, Integer> pointMap = new HashMap<Double, Integer>();            for (int j = 0; j < points.length; j++) {                if(j==i) continue;                if(points[i].y==points[j].y && points[i].x==points[j].x) {                    dup++;                    continue;                }                double grad = getGrad(points[i], points[j]);                if (!pointMap.containsKey(grad)) {                    pointMap.put(grad, 1);                                    }                else {                    pointMap.put(grad, pointMap.get(grad) + 1);                                    }                            }            if (pointMap.size() == 0) max=max > dup ? max : dup;            for (Double k : pointMap.keySet()) {                max = max < pointMap.get(k) + dup ? pointMap.get(k) + dup: max;                            }                    }        return max;    }        private double getGrad(Point a, Point b) {        int xDiff = a.x - b.x;        int yDiff = a.y - b.y;                if (xDiff == 0) return Double.MAX_VALUE;        return (double) yDiff / xDiff;                            } }

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