Add solutions

Author: martwz

src/leetcode/problem/guess_number.rs

@@ -5,7 +5,7 @@ impl Solution {
         1
     }
 
-    unsafe fn guessNumber(n: i32) -> i32 {
+    unsafe fn guess_umber(n: i32) -> i32 {
         let mut l = 0;
         let mut r = n;
 

src/leetcode/problem/perfect_squares.rs

@@ -0,0 +1,19 @@
+// 279. Perfect Squares, Medium
+// https://leetcode.com/problems/perfect-squares/
+impl Solution {
+    pub fn num_squares(n: i32) -> i32 {
+        let mut dp = vec![0; n as usize + 1];
+        for i in 1..=n as usize {
+            let mut min = i as i32;
+            let mut j = 1;
+            while j * j <= i {
+                min = std::cmp::min(min, dp[i - j * j] + 1);
+                j += 1;
+            }
+            dp[i] = min;
+        }
+        dp[n as usize]
+    }
+}
+
+struct Solution {}