implementation of linked-list-based stack in objective-c

object-c/08_stack/LinkedStack.h

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+//
+//  LinkedStack.h
+//  algo
+//
+//  Created by Wenru Dong on 2018/10/8.
+//  Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+//  Stack based upon linked list
+//  基于链表实现的栈
+
+#import <Foundation/Foundation.h>
+
+@interface LinkedStack : NSObject
+
+- (BOOL)isEmpty;
+- (void)push:(int)value;
+- (int)pop;
+
+@end

object-c/08_stack/LinkedStack.m

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+//
+//  LinkedStack.m
+//  algo
+//
+//  Created by Wenru Dong on 2018/10/8.
+//  Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+#import "LinkedStack.h"
+#import "ListNode.h"
+
+@implementation LinkedStack
+{
+    @private
+    ListNode* _top;
+}
+
+- (BOOL)isEmpty {
+    return _top == nil;
+}
+
+- (void)push:(int)value {
+    ListNode *newTop = [ListNode nodeWithValue:value];
+    newTop.next = _top;
+    _top = newTop;
+}
+
+- (int)pop {
+    if ([self isEmpty]) {
+        [NSException raise:NSRangeException format:@"The stack is empty."];
+    }
+    int value = _top.value;
+    _top = _top.next;
+    return value;
+}
+
+- (NSString *)debugDescription {
+    NSMutableString *info = [[NSMutableString alloc] init];
+    ListNode *current = _top;
+    while (current) {
+        [info appendString:[NSString stringWithFormat:@"%d]", current.value]];
+        current = current.next;
+    }
+    return [NSString stringWithString:info];
+}
+
+@end

object-c/08_stack/LinkedStackTests.m

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+//
+//  LinkedStackTests.m
+//  LinkedStackTests
+//
+//  Created by Wenru Dong on 2018/10/8.
+//  Copyright © 2018年 Wenru Dong. All rights reserved.
+//  
+
+#import <XCTest/XCTest.h>
+#import "LinkedStack.h"
+
+@interface LinkedStackTests : XCTestCase
+
+@end
+
+@implementation LinkedStackTests
+
+- (void)setUp {
+    [super setUp];
+    // Put setup code here. This method is called before the invocation of each test method in the class.
+}
+
+- (void)tearDown {
+    // Put teardown code here. This method is called after the invocation of each test method in the class.
+    [super tearDown];
+}
+
+- (void)testPush {
+    LinkedStack *stack = [[LinkedStack alloc] init];
+    for (int i = 0; i < 10; i++) {
+        [stack push:i];
+    }
+    XCTAssertEqualObjects([stack debugDescription], @"9]8]7]6]5]4]3]2]1]0]");
+}
+
+- (void)testPop {
+    LinkedStack *stack = [[LinkedStack alloc] init];
+    for (int i = 0; i < 10; i++) {
+        [stack push:i];
+    }
+    [stack pop];
+    XCTAssertEqualObjects([stack debugDescription], @"8]7]6]5]4]3]2]1]0]");
+    for (int i = 0; i < 9; i++) {
+        [stack pop];
+    }
+    XCTAssertThrowsSpecificNamed([stack pop], NSException, NSRangeException, @"The stack is empty.");
+}
+
+//- (void)testPerformanceExample {
+//    // This is an example of a performance test case.
+//    [self measureBlock:^{
+//        // Put the code you want to measure the time of here.
+//    }];
+//}
+
+@end

object-c/08_stack/ListNode.h

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+//
+//  ListNode.h
+//  algo
+//
+//  Created by Wenru Dong on 2018/10/6.
+//  Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface ListNode : NSObject
+
+@property int value;
+@property ListNode *next;
+
+- (instancetype)initWithValue:(int)value;
++ (instancetype)nodeWithValue:(int)value;
+
+@end

object-c/08_stack/ListNode.m

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+//
+//  ListNode.m
+//  algo
+//
+//  Created by Wenru Dong on 2018/10/6.
+//  Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+#import "ListNode.h"
+
+@implementation ListNode
+
+- (instancetype)initWithValue:(int)value {
+    if (self = [super init]) {
+        _value = value;
+    }
+    return self;
+}
+
++ (instancetype)nodeWithValue:(int)value {
+    return [[self alloc] initWithValue:value];
+}
+
+- (NSString*)debugDescription {
+    return [NSString stringWithFormat:@"%d", _value];
+}
+
+@end