103 lines
3.0 KiB
Objective-C
103 lines
3.0 KiB
Objective-C
#import "FourOperation.h"
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#import "ArrayStack.h"
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const NSDictionary *operationPriorityDict() {
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return @{@"*": @1, @"/": @1, @"+": @0, @"-": @0};
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}
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@implementation FourOperation {
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@private
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Stack *_optStack;
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Stack *_numStack;
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NSNumberFormatter *_numFormatter;
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}
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+ (FourOperation *)shared {
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static FourOperation* single = nil;
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static dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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single = [FourOperation new];
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});
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return single;
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}
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- (instancetype)init {
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self = [super init];
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_optStack = [[Stack alloc] initWithCapacity:100];
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_numStack = [[Stack alloc] initWithCapacity:100];
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_numFormatter = [NSNumberFormatter new];
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return self;
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}
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- (id)caculateExpression:(NSString *)expression {
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NSArray *elements = [expression componentsSeparatedByString:@" "];
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for (NSString *obj in elements) {
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NSNumber *numb = [_numFormatter numberFromString:obj];
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if (numb) { // 运算数
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[_numStack push:numb];
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} else { // 操作符
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// 如果栈顶操作符优先级大于等于当前操作符
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while ([self _topOperationPriorityIsHigherOrEqualToOperation:obj]) {
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// 取出栈顶的操作符和两个操作数做一次运算
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NSNumber *res = [self _excuteOnceCaculate];
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// 计算结果存入栈
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[_numStack push:res];
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}
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[_optStack push:obj];
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}
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}
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// 如果操作符存在栈中，依次取出做运算
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NSNumber *res = nil;
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while ([_optStack top]) {
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res = [self _excuteOnceCaculate];
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[_numStack push:res];
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}
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return res;
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}
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- (NSInteger)_getPriority:(NSString *)opt {
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return [[operationPriorityDict() objectForKey:opt] integerValue];
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}
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- (BOOL)_topOperationPriorityIsHigherOrEqualToOperation:(NSString *)opt {
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NSString *topOpt = [_optStack top];
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if (!topOpt) return NO;
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NSInteger curPriority = [self _getPriority:opt];
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NSInteger topPriority = [self _getPriority:topOpt];
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return curPriority <= topPriority;
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}
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- (NSNumber *)_excuteOnceCaculate {
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NSNumber *numRight = [_numStack pop];
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NSNumber *numLeft = [_numStack pop];
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NSString *topOpt = [_optStack pop];
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NSInteger result = [self _caculeteWithNumberLeft:numLeft numberRight:numRight operation:topOpt];
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NSNumber *res = [NSNumber numberWithInteger:result];
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return res;
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}
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- (NSInteger)_caculeteWithNumberLeft:(NSNumber *)numLeft numberRight:(NSNumber *)numRight operation:(NSString *)opt {
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if (!numLeft || !numRight || !opt) return 0;
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NSInteger left = [numLeft integerValue];
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NSInteger right = [numRight integerValue];
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if ([opt isEqualToString:@"+"]) {
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return left + right;
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} else if ([opt isEqualToString:@"-"]) {
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return left - right;
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} else if ([opt isEqualToString:@"*"]) {
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return left * right;
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} else if ([opt isEqualToString:@"/"]) {
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return left / right;
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} else {
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return 0;
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}
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}
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@end
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