rust sort

leetcode 976

给定由一些正数（代表长度）组成的数组 A，返回由其中三个长度组成的、面积不为零的三角形的最大周长。

如果不能形成任何面积不为零的三角形，返回 0。

 1 impl Solution {
 2     pub fn largest_perimeter(a: Vec<i32>) -> i32 {
 3         let mut a = a;
 4         a.sort_by(|a, b| b.cmp(&a));
 5         for i in 0..a.len()-2 {
 6             if a[i] < a[i+1] + a [i+2] {
 7                 return a[i] + a[i+1] + a[i+2];
 8             }
 9         }
10         0
11     }
12 }

sort_by源码

 1 /// # Examples
 2     ///
 3     /// ```
 4     /// let mut v = [5, 4, 1, 3, 2];
 5     /// v.sort_by(|a, b| a.cmp(b));
 6     /// assert!(v == [1, 2, 3, 4, 5]);
 7     ///
 8     /// // reverse sorting
 9     /// v.sort_by(|a, b| b.cmp(a));
10     /// assert!(v == [5, 4, 3, 2, 1]);
11     /// ```
12     #[stable(feature = "rust1", since = "1.0.0")]
13     #[inline]
14     pub fn sort_by<F>(&mut self, mut compare: F)
15         where F: FnMut(&T, &T) -> Ordering
16     {
17         merge_sort(self, |a, b| compare(a, b) == Less);
18     }