From ba9984fa27522c6452b678beb540efb655eb47dd Mon Sep 17 00:00:00 2001
From: GadHao <524472212@qq.com>
Date: Thu, 25 Nov 2021 15:55:13 +0800
Subject: [PATCH] feat: fix the error caused when the key does not exist in the
 array

---
 .../jimmysun/algorithms/chapter1_1/Ex29.java  | 79 ++++++++++++++-----
 1 file changed, 60 insertions(+), 19 deletions(-)

diff --git a/src/com/jimmysun/algorithms/chapter1_1/Ex29.java b/src/com/jimmysun/algorithms/chapter1_1/Ex29.java
index 602d4f3..e49ec58 100644
--- a/src/com/jimmysun/algorithms/chapter1_1/Ex29.java
+++ b/src/com/jimmysun/algorithms/chapter1_1/Ex29.java
@@ -4,37 +4,78 @@
 
 public class Ex29 {
 	public static int rank(int key, int[] a) {
-		int low = 0;
-		int high = a.length - 1;
-		while (low <= high) {
-			int mid = low + (high - low) / 2;
-			if (a[mid] == key) {
-				while (mid >= 0 && a[mid] == key){
-					mid--;
+		int lo = 0;
+		int hi = a.length - 1;
+
+		while (hi >= lo) {
+			int mid = lo + (hi - lo) / 2;
+			if (a[mid] >= key) {
+				if (mid == 0) {
+					return 0;
+				}
+				if (a[mid - 1] < key) {
+					return mid;
+				} else {
+					hi = mid - 1;
+				}
+			} else {
+				if (mid == a.length - 1) {
+					return a.length;
+				}
+
+				if (a[mid + 1] >= key) {
+					return mid + 1;
+				} else {
+					lo = mid + 1;
 				}
-				return ++mid;
-			} else if (a[mid] < key){
-				low = mid + 1;
-			} else if (a[mid] > key){
-				high =mid - 1;
 			}
 		}
-		return -1;
+
+		return 0;
 	}
 
 	public static int count(int key, int[] a) {
-		int num = 1;
-		int pos = rank(key, a);
-		while (pos < a.length - 1 && a[pos] == a[++pos]) {
-			num++;
+		int rank = rank(key, a);
+
+		if (rank == a.length || key != a[rank]) {
+			return 0;
 		}
-		return num;
+
+		int lo = rank;
+		int hi = a.length - 1;
+		int lastIndex = 0;
+
+		while (lo <= hi) {
+			int mid = lo + (hi - lo) / 2;
+			if (a[mid] > key) {
+				hi = mid - 1;
+			} else if (a[mid] < key) {
+				lo = mid + 1;
+			} else if (a[mid] == key) {
+				if (mid == a.length - 1) {
+					lastIndex = a.length - 1;
+					break;
+				}
+
+				if (a[mid + 1] > key) {
+					lastIndex = mid;
+					break;
+				} else {
+					lo = mid + 1;
+				}
+			}
+		}
+
+		return lastIndex - rank + 1;
 	}
 
 	public static void main(String[] args) {
-		int[] a = new int[] {84, 48, 68, 10, 18, 98, 12, 23, 54, 57, 33, 16, 77, 11, 29, 11, 29, 77, 77};
+		int[] a = new int[] { 84, 48, 68, 10, 18, 98, 12, 23, 54, 57, 33, 16, 77, 11, 29, 11, 29, 77, 77 };
 		Arrays.sort(a);
 		System.out.println(rank(29, a));
 		System.out.println(count(48, a));
+		// test the condition that the key not exist in the array
+		System.out.println(rank(14, a));
+		System.out.println(count(14, a));
 	}
 }