Longest Substring Without Repeating Characters，longestrepeating

Longest Substring Without Repeating Characters，longestrepeating

Longest  Substring Without Repeating Characters （来自LeetCode）

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.
 
解题思路：
历遍字符串，当当前字符出现过的时候，子串开始位置+1，否则更新locs数组中的hash值为当前位置。

//
//  ViewController.m
//  longestSubstring
//
//  Created by bcc_cae on 16/3/25.
//  Copyright © 2016年 bcc_cae. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSString *str = @"abcabcbb";
    int max = [self lengthOfLongestSubstring:str];
    
    NSLog(@"%d",max);
    
    
}

-(int)lengthOfLongestSubstring:(NSString *)s
{
    int locs[256];  //保存字符上一次出现的位置
    memset(locs, -1, sizeof(locs));
    
    int idx = -1,max = 0; //idx为当前子串的开始位置-1
    
    for (int i=0; i<s.length; i++) {
        unichar index =[s characterAtIndex:i];
        if (locs[index]>idx) {
            idx = locs[[s characterAtIndex:i]];
        }
        if (i-idx>max) {
            max = i -idx;
        }
        
        locs[index] =  i;
    }
    
    return max;
}


@end