Perfect Squares: BFS, O(n), could use math & reduce to O(sqrt(n)).

Author: DeanChensj

Medium/279_Perfect-Squares.cpp

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+#include "../Header.h"
+
+using namespace std;
+int numSquares(int n) {
+    bool *isVisited = new bool[n+1];
+    memset(isVisited, 0, n+1);
+    vector<int> squares;
+    queue<int> BFS;
+    for (int i = 1; i*i <= n; i++) {
+        int t = i*i;
+        if (t == n) return 1;
+        squares.push_back(t);
+        BFS.push(t);
+        isVisited[t] = 1;
+    }
+    int curLevelCnt = 0, curLevel = 1, preLevelCnt = squares.size();
+   
+    while(1) {
+        curLevel++;
+        while(preLevelCnt--) {
+            int num = BFS.front();
+            BFS.pop();
+            for (auto square: squares) {
+                int t = num + square;
+                if (t == n) return curLevel;
+                if (t > n) break;
+                if (!isVisited[t]) {
+                    curLevelCnt++;
+                    isVisited[t] = 1;
+                    BFS.push(t);
+                }
+                
+            }
+        }
+        preLevelCnt = curLevelCnt;
+    }
+}
+int main(int argc, char const *argv[])
+{
+    srand((int)time(NULL));
+	int num = random(9999);
+    cout << num << " " << numSquares(num) << endl;
+	return 0;
+}