LeetCode——Next Permutation

LeetCode——Next Permutation

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.
1,2,3 → 1,3,2
3,2,1 → 1,2,3
1,1,5 → 1,5,1

題目：實現 下一個排列，其按字典序重新排列給定數組為比下一個排列更大的排列。

思路：下一個排列實際上比當前排列大且最接近的排列。具體做法是：在數組中從後往前，找到最後升序的地方，交換前後值，並將後面的原序逆轉為升序。

	public void nextPermutation(int[] num) {
		int len = num.length, i = 0, j = 0;
		for (i = len - 2; i >= 0; i--) {
			if (num[i] >= num[i + 1])
				continue;
			for (j = len - 1; j > i; j--) {
				if (num[j] > num[i])
					break;
			}
			break;
		}
		if (i >= 0) {
			int temp = num[i];
			num[i] = num[j];
			num[j] = temp;
		}
		int end = len - 1;
		int start = i + 1;
		while (start < end) {
			int temp = num[start];
			num[start] = num[end];
			num[end] = temp;
			start++;
			end--;
		}
	}