287.find-the-duplicate-number-hashmap.go

/*
 * @lc app=leetcode id=287 lang=golang
 *
 * [287] Find the Duplicate Number
 *
 * https://leetcode.com/problems/find-the-duplicate-number/description/
 *
 * algorithms
 * Medium (47.88%)
 * Likes:    2349
 * Dislikes: 257
 * Total Accepted:    183.8K
 * Total Submissions: 372.7K
 * Testcase Example:  '[1,3,4,2,2]'
 *
 * Given an array nums containing n + 1 integers where each integer is between
 * 1 and n (inclusive), prove that at least one duplicate number must exist.
 * Assume that there is only one duplicate number, find the duplicate one.
 * 
 * Example 1:
 * 
 * 
 * Input: [1,3,4,2,2]
 * Output: 2
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: [3,1,3,4,2]
 * Output: 3
 * 
 * Note:
 * 
 * 
 * You must not modify the array (assume the array is read only).
 * You must use only constant, O(1) extra space.
 * Your runtime complexity should be less than O(n^2).
 * There is only one duplicate number in the array, but it could be repeated
 * more than once.
 * 
 * 
 */
// Time Complexity: O(n)
// Space Complexity: O(n)
func findDuplicate(nums []int) int {
    m := map[int]bool{}

    for _, num := range nums {
        if _, ok := m[num]; !ok {
            m[num] = true
        } else {
            return num
        }
    }

    return 0
}