daily problem

Author: StephenLeeUSTC

src/solution/mod.rs

@@ -29,3 +29,4 @@ mod s0508_most_frequent_subtree_sum;
 mod s1035_uncrossed_lines;
 mod s0169_majority_element;
 mod s0153_find_minimum_in_rotated_sorted_array;
+mod s0279_perfect_squares;

src/solution/s0279_perfect_squares.rs

@@ -0,0 +1,78 @@
+/**
+ * [279] Perfect Squares
+ *
+ * Given an integer n, return the least number of perfect square numbers that sum to n.
+ * A perfect square is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, 1, 4, 9, and 16 are perfect squares while 3 and 11 are not.
+ *  
+ * Example 1:
+ * 
+ * Input: n = 12
+ * Output: 3
+ * Explanation: 12 = 4 + 4 + 4.
+ * 
+ * Example 2:
+ * 
+ * Input: n = 13
+ * Output: 2
+ * Explanation: 13 = 4 + 9.
+ * 
+ *  
+ * Constraints:
+ * 
+ * 	1 <= n <= 10^4
+ * 
+ */
+pub struct Solution {}
+
+ // discuss: https://leetcode.com/problems/perfect-squares discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+use std::cmp::min;
+
+impl Solution {
+    pub fn num_squares(n: i32) -> i32 {
+        let mut nums = vec![];
+        for i in 1..n {
+            if i * i > n {
+                break;
+            } else {
+                nums.push(i * i);
+            }
+        }
+        // println!("nums is {:?}", nums);
+        let l = nums.len();
+        // indeed a package problem
+        // dp[i][j] = min(dp[i - 1][j - nums[i]] + 1) for nums[i] <= j
+        let mut dp = vec![vec![n; n as usize + 1]; l + 1];
+        for i in 0..=l as usize {
+            dp[i][0] = 0;
+        }
+
+        for i in 1..=l as usize {
+            for j in 1..=n as usize {
+                if nums[i - 1] <= j as i32 {
+                    dp[i][j] = min(dp[i][j - nums[i - 1] as usize] + 1, dp[i - 1][j]);
+                } else {
+                    dp[i][j] = dp[i - 1][j];
+                }
+                // println!("dp[{}][{}] is {}", i, j, dp[i][j]);
+            }
+        }
+
+        return dp[l as usize][n as usize];
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_279() {
+        assert_eq!(Solution::num_squares(9), 1);
+        assert_eq!(Solution::num_squares(12), 3);
+        assert_eq!(Solution::num_squares(13), 2);
+    }
+}