Given a non-negative integer N, find the largest number that is less than or equal to N with monotone increasing digits.
(Recall that an integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y.)
Example 1:
Input: N = 10
Output: 9
**Example 2:**
Input: N = 1234
Output: 1234
**Example 3:**
Input: N = 332
Output: 299
Note: N is an integer in the range [0, 10^9].
Hint:
要找小于或等于一个数的,最大的单调递增数(高位不大于低位),显然是个贪心问题。
我们知道,尽量保证高位不减少或降幅尽可能小,则数字越大。
我们应该去首先考虑去修改低位,使低位变大。
因此从个位开始,如果低位小于其前一个高位,将这个高位-1,而使低位变成最大的‘9’。
class Solution {
public:
int monotoneIncreasingDigits(int N) {
stringstream ss;
ss << N;
string num;
ss >> num;
int k = num.size();
for (int i = num.size()-1; i > 0; i--) {
if (num[i] < num[i-1]) {
k = i;
num[i-1] -= 1;
}
}
for (int i = k; i < num.size(); i++) {
num[i] = '9';
}
ss.clear();
ss << num;
ss >> N;
return N;
}
};