【一次过】Lintcode 1319. Contains Duplicate II

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Given an array of integers and an integer k, find out whether there are two distinct indices iand j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.

样例

Given nums = [1,2,1], k = 0, return false.

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解题思路：

由于与下标有关系，所以使用HashMap存储数组中的值与对应的下标，将数组依次扫描存储进Map中，当遇到有重复值时，判断这两值对应下标的绝对值差是否满足条件，满足则返回true，否则更新下标值，因为为了让对后面重复值与它的差尽可能最小，所以需要使其下标保持最前。

public class Solution {
    /**
     * @param nums: the given array
     * @param k: the given number
     * @return:  whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k
     */
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        // Write your code here
        Map<Integer,Integer> map = new HashMap<>();//key存储数组中的值，value存储对应值的下标
        
        for(int i=0 ; i<nums.length ; i++){
            if(!map.containsKey(nums[i])){ //如果此值第一次出现
                map.put(nums[i],i);
            }else{ //如果碰见相等的值
                int diff = Math.abs(map.get(nums[i]) - i); //相等值的下标绝对值差
                if(diff <= k)
                    return true;
                else
                    map.put(nums[i],i); //更新下标
            }
        }
        
        return false;
    }
}