solves perfect squares in java

Author: anishLearnsToCode

src/PerfectSquares.java

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+// https://leetcode.com/problems/perfect-squares
+// T: O(N * k) k = size of perfect squares array which is constant
+// S: O(N + k)
+
+public class PerfectSquares {
+    private static final int[] PERFECT_SQUARES = {
+            1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576,
+            625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849,
+            1936, 2025, 2116, 2209, 2304, 2401, 2500, 2601, 2704, 2809, 2916, 3025, 3136, 3249, 3364, 3481, 3600, 3721,
+            3844, 3969, 4096, 4225, 4356, 4489, 4624, 4761, 4900, 5041, 5184, 5329, 5476, 5625, 5776, 5929, 6084, 6241,
+            6400, 6561, 6724, 6889, 7056, 7225, 7396, 7569, 7744, 7921, 8100, 8281, 8464, 8649, 8836, 9025, 9216, 9409,
+            9604, 9801, 10000, 10_201
+    };
+
+    public int numSquares(int n) {
+        final int[] dp = new int[n + 1];
+        dp[0] = dp[1] = 1;
+        for (int i = 2 ; i < dp.length ; i++) {
+            dp[i] = numSquares(i, dp);
+        }
+        return dp[dp.length - 1];
+    }
+
+    private int numSquares(int n, int[] dp) {
+        int result = Integer.MAX_VALUE, square;
+        for (int i = 0 ; PERFECT_SQUARES[i] <= n ; i++) {
+            square = PERFECT_SQUARES[i];
+            result = Math.min(result, dp[square] + dp[n - square]);
+        }
+        return result;
+    }
+}