By

Tow Num

给定一个整数数组，返回两个数的和为指定目标的索引
时间复杂度 O(n)
e.g:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
leetcode

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/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
// 1>
function twoSum(nums, target){
    for(var i = 0, len = nums.length; i < len; i++){
        if(target >= nums[i]){
            for(var j = i; j < len; j++){
                if(target === nums[i] + nums[j]){
                    return [i, j];
                }
            }
        }
    }
    return [];
};
// 2>
function twoSum(nums, target){
    var index;
    for(var i = 0, len = nums.length; i < len; i++){
        if(target >= nums[i]){
            index = nums.indexOf(target - nums[i]);
            if(index !== -1 && index > i){
                return [i, index];
            }
        }
    }
    return [];
};
// 3> 用对象缓存当前元素
function twoSum(nums, target){
    var temp = {};
    var res = [];
    for(var i = 0, len = nums.length; i < len; i++){
        if(target >= nums[i]){
            if(temp[target - nums[i]] !== undefined){
                return [temp[target - nums[i]], i];
            }else {
                temp[nums[i]] = i;
            }
        }
    }

    return [];
};

console.log(twoSum([1, 2, 3, 4, 5, 6, 7], 9));