497 finish

Author: aQua

Algorithms/0497.random-point-in-non-overlapping-rectangles/README.md

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+# [497. Random Point in Non-overlapping Rectangles](https://leetcode.com/problems/random-point-in-non-overlapping-rectangles/)
+
+## 题目
+
+Given a list of non-overlapping axis-aligned rectangles rects, write a function pick which randomly and uniformily picks an integer point in the spacecovered by the rectangles.
+
+Note:
+
+1. An integer pointis a point that has integer coordinates.
+1. A pointon the perimeterof a rectangle isincluded in the space covered by the rectangles.
+1. ith rectangle = rects[i] =[x1,y1,x2,y2], where [x1, y1]are the integer coordinates of the bottom-left corner, and [x2, y2]are the integer coordinates of the top-right corner.
+1. length and width of each rectangle does not exceed 2000.
+1. 1 <= rects.length<= 100
+1. pick return a point as an array of integer coordinates[p_x, p_y]
+1. pick is called at most 10000times.
+
+Example 1:
+
+```text
+Input:
+["Solution","pick","pick","pick"]
+[[[[1,1,5,5]]],[],[],[]]
+Output:
+[null,[4,1],[4,1],[3,3]]
+```
+
+Example 2:
+
+```text
+Input:
+["Solution","pick","pick","pick","pick","pick"]
+[[[[-2,-2,-1,-1],[1,0,3,0]]],[],[],[],[],[]]
+Output:
+[null,[-1,-2],[2,0],[-2,-1],[3,0],[-2,-2]]
+```
+
+Explanation of Input Syntax:
+
+The input is two lists:the subroutines calledand theirarguments.Solution'sconstructor has one argument, the array of rectangles rects. pickhas no arguments.Argumentsarealways wrapped with a list, even if there aren't any.
+
+## 解题思路
+
+见程序注释

Algorithms/0497.random-point-in-non-overlapping-rectangles/random-point-in-non-overlapping-rectangles.go

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+package problem0497
+
+import (
+	"math/rand"
+	"sort"
+)
+
+// Solution object will be instantiated and called as such:
+// obj := Constructor(rects);
+// param_1 := obj.Pick();
+type Solution struct {
+	total  int   // 所有可能离散的点的个数
+	counts []int // count[i] 记录了前 i 个矩形中所有点的个数
+	rects  [][]int
+}
+
+// Constructor 创建 Solution
+func Constructor(rects [][]int) Solution {
+	size := len(rects)
+
+	total := 0
+	counts := make([]int, size)
+	tmp := make([][]int, size)
+
+	for i, r := range rects {
+		x1, y1, x2, y2 := r[0], r[1], r[2], r[3]
+		w, h := x2-x1+1, y2-y1+1 // +1 是因为 [a,b] 之间一共有 b-a+1 个离散的点
+		total += w * h
+		counts[i] = total
+		tmp[i] = []int{x1, y1, w, h} // 修改 rect 的表达方式
+	}
+
+	return Solution{
+		counts: counts,
+		rects:  tmp,
+		total:  total,
+	}
+}
+
+// Pick 返回正方形内的点
+func (s *Solution) Pick() []int {
+	cand := rand.Intn(s.total)
+	// 根据 cand 找到需要返回那个矩形下的点
+	i := sort.SearchInts(s.counts, cand)
+
+	x1, y1, w, h := s.rects[i][0], s.rects[i][1], s.rects[i][2], s.rects[i][3]
+
+	x := x1 + rand.Intn(w)
+	y := y1 + rand.Intn(h)
+
+	return []int{x, y}
+}

Algorithms/0497.random-point-in-non-overlapping-rectangles/random-point-in-non-overlapping-rectangles_test.go

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+package problem0497
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Solution(t *testing.T) {
+	ast := assert.New(t)
+
+	rects := [][]int{
+		[]int{1, 1, 5, 5},
+	}
+
+	s := Constructor(rects)
+
+	for i := 0; i < 10000; i++ {
+		p := s.Pick()
+		actual := 0
+		for _, r := range rects {
+			if isWithin(r, p) {
+				actual++
+			}
+		}
+		ast.Equal(1, actual)
+	}
+}
+
+func Test_Solution_2(t *testing.T) {
+	ast := assert.New(t)
+
+	rects := [][]int{
+		{-2, -2, -1, -1},
+		{1, 0, 3, 0},
+	}
+
+	s := Constructor(rects)
+
+	for i := 0; i < 10000; i++ {
+		p := s.Pick()
+		actual := 0
+		for _, r := range rects {
+			if isWithin(r, p) {
+				actual++
+			}
+		}
+		ast.Equal(1, actual)
+	}
+}
+
+func isWithin(rect, point []int) bool {
+	x1, y1, x2, y2 := rect[0], rect[1], rect[2], rect[3]
+	x, y := point[0], point[1]
+
+	return x1 <= x && x <= x2 &&
+		y1 <= y && y <= y2
+}

leetcode.json

@@ -1,7 +1,7 @@
 {
 	"Username": "aQuaYi",
 	"Ranking": 869,
-	"Updated": "2018-08-04T21:14:48.409930646+08:00",
+	"Updated": "2018-08-04T21:16:55.918544895+08:00",
 	"Record": {
 		"Easy": {
 			"Solved": 180,