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package class14;
// 测试链接：https://leetcode.com/problems/first-missing-positive/
public class Code06_MissingNumber {
public static int firstMissingPositive(int[] arr) {
// l是盯着的位置
// 0 ~ L-1有效区
int L = 0;
int R = arr.length;
while (L != R) {
if (arr[L] == L + 1) {
L++;
} else if (arr[L] <= L || arr[L] > R || arr[arr[L] - 1] == arr[L]) { // 垃圾的情况
swap(arr, L, --R);
} else {
swap(arr, L, arr[L] - 1);
}
return L + 1;
public static void swap(int[] arr, int i, int j) {
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
