279 - Perfect Squares
#medium
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.
class Solution {
public:
int numSquares(int n) {
// 使用bfs
queue<int> que;
unordered_set<int> visited;
que.push( 0 );
int result = 0;
while ( !que.empty() ) {
int que_size = que.size();
result++;
for ( int i = 0; i < que_size; i++ ) {
int cur = que.front();
que.pop();
for ( int j = 1; cur < n; j++ ) {
int sum = cur + j*j;
if ( sum == n ) return result;
else if ( sum > n ) break;
else {
if ( !visited.count(sum) ) {
que.push( sum );
visited.insert( sum );
}
}
}
}
}
return result;
}
};