diff --git a/src/class29/Code01_FindMinKth.java b/src/class29/Code01_FindMinKth.java
index aefb6d9..e317550 100644
--- a/src/class29/Code01_FindMinKth.java
+++ b/src/class29/Code01_FindMinKth.java
@@ -30,6 +30,7 @@ public class Code01_FindMinKth {
 	}
 
 	// 改写快排，时间复杂度O(N)
+	// k >= 1
 	public static int minKth2(int[] array, int k) {
 		int[] arr = copyArray(array);
 		return process2(arr, 0, arr.length - 1, k - 1);
@@ -53,10 +54,6 @@ public class Code01_FindMinKth {
 		}
 		// 不止一个数  L +  [0, R -L]
 		int pivot = arr[L + (int) (Math.random() * (R - L + 1))];
-		
-		// range[0] range[1]
-		//  L   ..... R     pivot 
-		//  0         1000     70...800
 		int[] range = partition(arr, L, R, pivot);
 		if (index >= range[0] && index <= range[1]) {
 			return arr[index];
@@ -100,6 +97,10 @@ public class Code01_FindMinKth {
 		if (L == R) {
 			return arr[L];
 		}
+		// L...R  每五个数一组
+		// 每一个小组内部排好序
+		// 小组的中位数组成新数组
+		// 这个新数组的中位数返回
 		int pivot = medianOfMedians(arr, L, R);
 		int[] range = partition(arr, L, R, pivot);
 		if (index >= range[0] && index <= range[1]) {
diff --git a/src/class29/Code03_ReservoirSampling.java b/src/class29/Code03_ReservoirSampling.java
index e4d0710..c2ce9e3 100644
--- a/src/class29/Code03_ReservoirSampling.java
+++ b/src/class29/Code03_ReservoirSampling.java
@@ -38,7 +38,38 @@ public class Code03_ReservoirSampling {
 
 	}
 
+	// 请等概率返回1~i中的一个数字
+	public static int random(int i) {
+		return (int) (Math.random() * i) + 1;
+	}
+
 	public static void main(String[] args) {
+		System.out.println("hello");
+		int test = 10000;
+		int ballNum = 17;
+		int[] count = new int[ballNum + 1];
+		for (int i = 0; i < test; i++) {
+			int[] bag = new int[10];
+			int bagi = 0;
+			for (int num = 1; num <= ballNum; num++) {
+				if (num <= 10) {
+					bag[bagi++] = num;
+				} else { // num > 10
+					if (random(num) <= 10) { // 一定要把num球入袋子
+						bagi = (int) (Math.random() * 10);
+						bag[bagi] = num;
+					}
+				}
+
+			}
+			for (int num : bag) {
+				count[num]++;
+			}
+		}
+		for (int i = 0; i <= ballNum; i++) {
+			System.out.println(count[i]);
+		}
+
 		System.out.println("hello");
 		int all = 100;
 		int choose = 10;