56 Height Checker

题目

Students are asked to stand in non-decreasing order of heights for an annual photo.

Return the minimum number of students that must move in order for all students to be standing in non-decreasing order of height.

Notice that when a group of students is selected they can reorder in any possible way between themselves and the non selected students remain on their seats.

Example 1:

Input: heights = [1,1,4,2,1,3]
Output: 3
Explanation:
Current array : [1,1,4,2,1,3]
Target array : [1,1,1,2,3,4]
On index 2 (0-based) we have 4 vs 1 so we have to move this student.
On index 4 (0-based) we have 1 vs 3 so we have to move this student.
On index 5 (0-based) we have 3 vs 4 so we have to move this student.

Example 2:

Input: heights = [5,1,2,3,4]
Output: 5

Example 3:

Input: heights = [1,2,3,4,5]
Output: 0

Constraints:

1 <= heights.length <= 100
1 <= heights[i] <= 100

分析

题意：给定一个数组，返回将其升序排序所需的最小移动步数。

脑筋急转弯！
事实上我们只需要比较排序前和排序后对应位置的数不同的个数即可。
比如
14235 排序得到12345
相同位置不同数的个数为3

解答

class Solution {
    public int heightChecker(int[] heights) {
    	// 备份一个未排序的
        int[] tmp = Arrays.copyOf(heights,heights.length);
        // 排序
        Arrays.sort(heights);
        int res=0;
        // 求出不同的个数
        for(int i=0;i<heights.length;++i){
            if(tmp[i]!=heights[i]) res++;
        }
        return res;
    }
}