LeetCode: First Missing Positive

一开始有失误，发现如果外面定义了int ret， for循环里第一个条件为int ret = 1的话，这里的ret跟外面的ret不一样。少数次过

class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        map<int, int> s;
        int maxs = 0;
        for (int i = 0; i < n; i++) {
            maxs = max(maxs, A[i]);
            s[A[i]] = 1;
        }
        int ret = 1;
        for (ret = 1; ret <= maxs; ret++) {
            if (s.count(ret) == 0)  break;
        }
        return ret;
    }
};

 上面代码有错，题目要求是constant memory，下面这段代码是正确的

class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        for (int i = 0; i < n; i++) 
            if (A[i] != i+1) 
                while (A[i] > 0 && A[i] < n && A[A[i]-1] != A[i]) swap(A[i], A[A[i]-1]);
        for (int i = 0; i < n; i++) 
            if (A[i] != i+1) return i+1;
        return n+1;
    }
};

 C#:没有swap函数，注意swap的顺序

public class Solution {
    public int FirstMissingPositive(int[] nums) {
        for (int i = 0; i < nums.Length; i++) {
            if (nums[i] != i + 1) {
                while (nums[i] > 0 && nums[i] < nums.Length && nums[nums[i] - 1] != nums[i]) {
                    int tmp = nums[nums[i] - 1];
                    nums[nums[i] - 1] = nums[i];
                    nums[i] = tmp;
                }
            }
        }
        for (int i = 0; i < nums.Length; i++)
            if (nums[i] != i + 1) return i + 1;
        return nums.Length + 1;
    }
}