题解 | #缺失的第一个正整数# [S-P1]

[S-P3]: 由于不重复，缺少的正整数值属于[1, n+1], e.g.
[1,2,3,4,5] => 6
[1,2,3,4,6] => 5

import java.util.*;

// 缺少的正整数值属于[1, n+1]
public class Solution {
    public int minNumberDisappeared (int[] nums) {
      int n = nums.length;
      for (int i = 0; i < n; i++) {
        while (nums[i] != i+1 && nums[i] > 0 && nums[i] <= n) {
          // e.g. if nums[0] = 3, swap nums[0] with nums[3-1=2]
          swap(i, nums[i]-1, nums);
        }
      }
  
      for (int i = 0; i < n; i++) {
        if (nums[i] != i+1) return i+1;
      }
      
      return n+1;
    }
  
    void swap(int i, int j, int[] nums) {
      int tmp = nums[i];
      nums[i] = nums[j];
      nums[j] = tmp;
    }
}