LeetCode-1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

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Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

思路

利用hashmap,key存放数值,value存放出现的位置。从前到后进行遍历,将target值减去当前的值,看是否存在map中,若存在map中则取出相应的标号,退出。

代码

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public int[] twoSum(int[] nums, int target) {
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
int result[] = new int[2];
for (int i = 0; i < nums.length; i++){
int num = target - nums[i];
if(map.containsKey(num)){
result[0] = map.get(num);
result[1] = i;
return result;
}
map.put(nums[i], i);
}
return result;
}

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