CodeForces 490E Restoring Increasing Sequence

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题意：

一个严格递增序列某些数字的某些位被盖住了求恢复后的序列

思路：

贪心让每个数在大于前一个的基础上尽量的小
先讨论数字长度
len[i]<len[i-1] 一定是NO
len[i]>len[i-1] 除了第一位如果是？就填1以外其他？全填0
len[i]==len[i-1] dfs搜索num[i]格式下大于num[i-1]的最小的数

代码：

#include<cstdio>#include<iostream>#include<cstring>#include<string>#include<algorithm>#include<map>#include<set>#include<vector>#include<queue>#include<cstdlib>#include<ctime>#include<cmath>using namespace std;typedef long long LL;#define N 100010int n, ans = 1;char a[N][10];int len[N];bool dfs(int i, int j, int big) {    if (j == len[i]) {        if (big)            return true;        return false;    }    if (a[i][j] != '?') {        if (!big && a[i][j] < a[i - 1][j])            return false;        return dfs(i, j + 1, big | (a[i][j] > a[i - 1][j]));    } else {        if (big) {            a[i][j] = '0';            if (dfs(i, j + 1, 1))                return true;            a[i][j] = '?';            return false;        } else {            for (char k = a[i - 1][j]; k <= '9'; k++) {                a[i][j] = k;                if (dfs(i, j + 1, k > a[i - 1][j]))                    return true;            }            a[i][j] = '?';            return false;        }    }}int main() {    scanf("%d", &n);    for (int i = 1; i <= n; i++) {        scanf("%s", a[i]);        len[i] = strlen(a[i]);    }    for (int i = 1; i <= n; i++) {        if (len[i] < len[i - 1]) {            ans = 0;            break;        } else if (len[i] == len[i - 1]) {            if (!dfs(i, 0, 0)) {                ans = 0;                break;            }        } else {            if (a[i][0] == '?')                a[i][0] = '1';            for (int j = 1; j < len[i]; j++) {                if (a[i][j] == '?')                    a[i][j] = '0';            }        }    }    if (ans) {        puts("YES");        for (int i = 1; i <= n; i++)            puts(a[i]);    } else        puts("NO");    return 0;}

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