给定一个整数数组 nums 和一个目标值 target,请你在该数组中找出和为目标值的那 两个 整数,并返回他们的数组下标。
你可以假设每种输入只会对应一个答案。但是,数组中同一个元素不能使用两遍。
示例:
给定 nums = [2, 7, 11, 15], target = 9
因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]
- 暴力遍历
var twoSum = function(nums, target) {
var result = [];
for (var i = 0; i < nums.length; i++) {
for (var j = i + 1; j < nums.length; j++) {
if (nums[i] + nums[j] === target) {
return [i, j];
}
}
}
};
- 哈希映射
var twoSum = function(nums, target) {
var hashTable = [];
for (var i = 0; i < nums.length; i++) {
var diff = target - nums[i];
if (hashTable[diff] !== undefined) {
return [hashTable[diff], i];
}
hashTable[nums[i]] = i;
}
};
![两数之和 1 1603787763 1](https://assets.gnixner.com/wp-content/uploads/2020/10/1603787763-1.png)
![两数之和 2 1603787772 2](https://assets.gnixner.com/wp-content/uploads/2020/10/1603787772-2.png)
![两数之和 3 1603787772 3](https://assets.gnixner.com/wp-content/uploads/2020/10/1603787772-3.png)
![两数之和 4 1603787772 4](https://assets.gnixner.com/wp-content/uploads/2020/10/1603787772-4.png)
参考:https://leetcode-cn.com/problems/two-sum/solution/jie-suan-fa-1-liang-shu-zhi-he-by-guanpengchn/
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