Leetcode 279. Perfect Squares

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Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.

计算一个数最少由多少个完全平方数相加而成。

简单DP，从1开始向上转移。

class Solution {
public:
    int numSquares(int n) {
        vector<int> dp(n + 1, INT_MAX);
        dp[0] = 0;
        for(int i = 1; i <= n; i++ )
            for(int j = 1; j <= sqrt(i); j++)
                dp[i] = min(dp[i], dp[i - j * j] + 1);
        return dp[n];
    }
};