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两数之和

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;
    }
};




参考:https://leetcode-cn.com/problems/two-sum/solution/jie-suan-fa-1-liang-shu-zhi-he-by-guanpengchn/

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