First Missing Positive

最新推荐文章于 2025-04-26 14:16:51 发布

最新推荐文章于 2025-04-26 14:16:51 发布 · 80 阅读

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本文介绍了一种在未排序整数数组中寻找第一个缺失正整数的算法，该算法能在O(n)时间内运行并使用常数空间。通过具体实例展示了如何通过交换元素来定位缺失值。

Given an unsorted integer array, find the first missing positive integer.

For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.

Your algorithm should run in O(n) time and uses constant space.

public class Solution {
    public int firstMissingPositive(int[] nums) {
        int left = 0;
        int right = nums.length;
        while (left < right) {
        	if (nums[left] == left + 1) {
        		left++;
        	} else if (nums[left] <= left || nums[left] > right || nums[left] == nums[nums[left]-1]) {
        		nums[left] = nums[--right];
        	} else {
        		swap(nums, left, nums[left]-1);
        	}
        }
        return left + 1;
    }

	private void swap(int[] nums, int i, int j) {
		// TODO Auto-generated method stub
		int tmp = nums[i];
		nums[i] = nums[j];
		nums[j] = tmp;
	}
}