From 2848a3dc5d1859c6ae5e6c8b8a404ca5cd6da425 Mon Sep 17 00:00:00 2001
From: ParkFeng <1351315441@qq.com>
Date: Sat, 8 Dec 2018 00:40:38 +0800
Subject: [PATCH] second commit

---
 ParkFeng/random_pick_with_weight/Learn1.java | 43 ++++++++++++++++++++
 ParkFeng/random_pick_with_weight/readme.md   | 41 +++++++++++++++++++
 ParkFeng/readme.md                           |  4 +-
 3 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 ParkFeng/random_pick_with_weight/Learn1.java
 create mode 100644 ParkFeng/random_pick_with_weight/readme.md

diff --git a/ParkFeng/random_pick_with_weight/Learn1.java b/ParkFeng/random_pick_with_weight/Learn1.java
new file mode 100644
index 0000000..6624755
--- /dev/null
+++ b/ParkFeng/random_pick_with_weight/Learn1.java
@@ -0,0 +1,43 @@
+
+class Solution {
+
+    int[] arr;
+    int maxOfArr;
+    Random random = new Random();
+    public Solution(int[] w) {
+        arr = new int[w.length];
+        arr[0] = w[0];
+        for (int i = 1; i <arr.length; i++) {
+            arr[i] = arr[i-1]+w[i];
+        }
+        maxOfArr = arr[arr.length-1];
+    }
+
+    public int pickIndex() {
+        int rand = random.nextInt(maxOfArr)+1;
+        int index = findIndex(arr, rand);
+        return index;
+    }
+
+    private int findIndex(int[] nums, int m) {
+        int start = 0;
+        int end = nums.length-1;
+        while (start+1 < end) {
+            int mid = (start+end)/2;
+            if (nums[mid] == m) {
+                return mid;
+            } else if (nums[mid] < m) {
+                start = mid+1;
+            } else {
+                end = mid-1;
+            }
+        }
+        if (m > nums[end]) {
+            return end+1;
+        } else if (m > nums[start]) {
+            return start+1;
+        } else {
+            return start;
+        }
+    }
+}
\ No newline at end of file
diff --git a/ParkFeng/random_pick_with_weight/readme.md b/ParkFeng/random_pick_with_weight/readme.md
new file mode 100644
index 0000000..9199e8d
--- /dev/null
+++ b/ParkFeng/random_pick_with_weight/readme.md
@@ -0,0 +1,41 @@
+题目：
+
+给定一个正整数数组 w ，其中 w[i] 代表位置 i 的权重，请写一个函数 pickIndex ，它可以随机地获取位置 i，
+选取位置 i 的概率与 w[i] 成正比。
+
+说明:
+
+1 <= w.length <= 10000
+1 <= w[i] <= 10^5
+pickIndex 将被调用不超过 10000 次
+示例1:
+
+输入: 
+["Solution","pickIndex"]
+[[[1]],[]]
+输出: [null,0]
+示例2:
+
+输入: 
+["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
+[[[1,3]],[],[],[],[],[]]
+输出: [null,0,1,1,1,0]
+输入语法说明：
+
+输入是两个列表：调用成员函数名和调用的参数。Solution 的构造函数有一个参数，即数组 w。
+               pickIndex 没有参数。输入参数是一个列表，即使参数为空，也会输入一个 [] 空列表。
+               
+
+题目分析：
+
+1、该题针对：正整数数组---权重数组
+
+2、权重随机理解：
+eg: int[] arr = {3,4}--->向上抛一个硬币（假设硬币落地一定是平躺）7次，出现正面反面的次数（权重）分别为3,4，那么就可以说这个实验中正面出现概率是
+3/7，反面出现概率是4/7，回到已知的这个数组上，3+4=7，权重随机我们可以理解为一个箱子中有七个分别标有1~7数字的乒乓球，我们随机从
+箱子中每次拿一个乒乓球，那么拿到标有1，2，3的乒乓球我们就认为对应的是数组中的3，拿到4，5，6，7就对应的是4
+
+3、获取位置序号：利用二分法去查找
+
+
+
diff --git a/ParkFeng/readme.md b/ParkFeng/readme.md
index 48ff99f..e1d1353 100644
--- a/ParkFeng/readme.md
+++ b/ParkFeng/readme.md
@@ -2,4 +2,6 @@
 
 
 
-1.对角线遍历分析
\ No newline at end of file
+1.对角线遍历分析
+
+2.按权重随机选择
\ No newline at end of file