Leetcode-Java(二十八)

278. First Bad Version

二分查找的思路

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int left = 1;
        int right = n;
        while(left <= right){
            int mid = (right - left) / 2 + left;
            if(isBadVersion(mid)==true)
                right = mid - 1;
            else
                left = mid + 1;
        }
        return left;
    }
}

279. Perfect Squares

使用动态规划的方法，注意 dp[0] = 0这一步。

class Solution {
    public int numSquares(int n) {
        int[] dp = new int[n+1];
        Arrays.fill(dp,Integer.MAX_VALUE);
        dp[0] = 0;
        for(int i=0;i<=n;i++){
            for(int j=1;i + j * j <= n;j++){
                dp[i+j*j] = Math.min(dp[i] + 1,dp[i+j*j]);
            }
        }
        return dp[n];
    }
}